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rails--rails/activerecord/lib/active_record/associations.rb

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require 'active_support/core_ext/enumerable'
require 'active_support/core_ext/string/conversions'
require 'active_support/core_ext/module/remove_method'
require 'active_record/errors'
module ActiveRecord
class AssociationNotFoundError < ConfigurationError #:nodoc:
def initialize(record, association_name)
super("Association named '#{association_name}' was not found on #{record.class.name}; perhaps you misspelled it?")
end
end
class InverseOfAssociationNotFoundError < ActiveRecordError #:nodoc:
def initialize(reflection, associated_class = nil)
super("Could not find the inverse association for #{reflection.name} (#{reflection.options[:inverse_of].inspect} in #{associated_class.nil? ? reflection.class_name : associated_class.name})")
end
end
class HasManyThroughAssociationNotFoundError < ActiveRecordError #:nodoc:
def initialize(owner_class_name, reflection)
super("Could not find the association #{reflection.options[:through].inspect} in model #{owner_class_name}")
end
end
class HasManyThroughAssociationPolymorphicSourceError < ActiveRecordError #:nodoc:
def initialize(owner_class_name, reflection, source_reflection)
super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' on the polymorphic object '#{source_reflection.class_name}##{source_reflection.name}' without 'source_type'. Try adding 'source_type: \"#{reflection.name.to_s.classify}\"' to 'has_many :through' definition.")
end
end
class HasManyThroughAssociationPolymorphicThroughError < ActiveRecordError #:nodoc:
def initialize(owner_class_name, reflection)
super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
end
end
class HasManyThroughAssociationPointlessSourceTypeError < ActiveRecordError #:nodoc:
def initialize(owner_class_name, reflection, source_reflection)
super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' with a :source_type option if the '#{reflection.through_reflection.class_name}##{source_reflection.name}' is not polymorphic. Try removing :source_type on your association.")
end
end
class HasOneThroughCantAssociateThroughCollection < ActiveRecordError #:nodoc:
def initialize(owner_class_name, reflection, through_reflection)
super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' where the :through association '#{owner_class_name}##{through_reflection.name}' is a collection. Specify a has_one or belongs_to association in the :through option instead.")
end
end
class HasOneAssociationPolymorphicThroughError < ActiveRecordError #:nodoc:
def initialize(owner_class_name, reflection)
super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
end
end
class HasManyThroughSourceAssociationNotFoundError < ActiveRecordError #:nodoc:
def initialize(reflection)
through_reflection = reflection.through_reflection
source_reflection_names = reflection.source_reflection_names
source_associations = reflection.through_reflection.klass._reflections.keys
super("Could not find the source association(s) #{source_reflection_names.collect{ |a| a.inspect }.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)} in model #{through_reflection.klass}. Try 'has_many #{reflection.name.inspect}, :through => #{through_reflection.name.inspect}, :source => <name>'. Is it one of #{source_associations.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)}?")
end
end
class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ActiveRecordError #:nodoc:
def initialize(owner, reflection)
super("Cannot modify association '#{owner.class.name}##{reflection.name}' because the source reflection class '#{reflection.source_reflection.class_name}' is associated to '#{reflection.through_reflection.class_name}' via :#{reflection.source_reflection.macro}.")
end
end
class HasManyThroughCantAssociateNewRecords < ActiveRecordError #:nodoc:
def initialize(owner, reflection)
super("Cannot associate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to create the has_many :through record associating them.")
end
end
class HasManyThroughCantDissociateNewRecords < ActiveRecordError #:nodoc:
def initialize(owner, reflection)
super("Cannot dissociate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to delete the has_many :through record associating them.")
end
end
class HasManyThroughNestedAssociationsAreReadonly < ActiveRecordError #:nodoc:
def initialize(owner, reflection)
super("Cannot modify association '#{owner.class.name}##{reflection.name}' because it goes through more than one other association.")
end
end
class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
def initialize(reflection)
super("Cannot eagerly load the polymorphic association #{reflection.name.inspect}")
end
end
class ReadOnlyAssociation < ActiveRecordError #:nodoc:
def initialize(reflection)
super("Cannot add to a has_many :through association. Try adding to #{reflection.through_reflection.name.inspect}.")
end
end
# This error is raised when trying to destroy a parent instance in N:1 or 1:1 associations
# (has_many, has_one) when there is at least 1 child associated instance.
# ex: if @project.tasks.size > 0, DeleteRestrictionError will be raised when trying to destroy @project
class DeleteRestrictionError < ActiveRecordError #:nodoc:
def initialize(name)
super("Cannot delete record because of dependent #{name}")
end
end
# See ActiveRecord::Associations::ClassMethods for documentation.
module Associations # :nodoc:
extend ActiveSupport::Autoload
extend ActiveSupport::Concern
# These classes will be loaded when associations are created.
# So there is no need to eager load them.
autoload :Association, 'active_record/associations/association'
autoload :SingularAssociation, 'active_record/associations/singular_association'
autoload :CollectionAssociation, 'active_record/associations/collection_association'
autoload :CollectionProxy, 'active_record/associations/collection_proxy'
autoload :BelongsToAssociation, 'active_record/associations/belongs_to_association'
autoload :BelongsToPolymorphicAssociation, 'active_record/associations/belongs_to_polymorphic_association'
autoload :HasManyAssociation, 'active_record/associations/has_many_association'
autoload :HasManyThroughAssociation, 'active_record/associations/has_many_through_association'
autoload :HasOneAssociation, 'active_record/associations/has_one_association'
autoload :HasOneThroughAssociation, 'active_record/associations/has_one_through_association'
autoload :ThroughAssociation, 'active_record/associations/through_association'
module Builder #:nodoc:
autoload :Association, 'active_record/associations/builder/association'
autoload :SingularAssociation, 'active_record/associations/builder/singular_association'
autoload :CollectionAssociation, 'active_record/associations/builder/collection_association'
autoload :BelongsTo, 'active_record/associations/builder/belongs_to'
autoload :HasOne, 'active_record/associations/builder/has_one'
autoload :HasMany, 'active_record/associations/builder/has_many'
autoload :HasAndBelongsToMany, 'active_record/associations/builder/has_and_belongs_to_many'
end
eager_autoload do
autoload :Preloader, 'active_record/associations/preloader'
autoload :JoinDependency, 'active_record/associations/join_dependency'
autoload :AssociationScope, 'active_record/associations/association_scope'
autoload :AliasTracker, 'active_record/associations/alias_tracker'
end
# Clears out the association cache.
def clear_association_cache #:nodoc:
@association_cache.clear if persisted?
end
# :nodoc:
attr_reader :association_cache
# Returns the association instance for the given name, instantiating it if it doesn't already exist
def association(name) #:nodoc:
association = association_instance_get(name)
if association.nil?
raise AssociationNotFoundError.new(self, name) unless reflection = self.class._reflect_on_association(name)
association = reflection.association_class.new(self, reflection)
association_instance_set(name, association)
end
association
end
private
# Returns the specified association instance if it responds to :loaded?, nil otherwise.
def association_instance_get(name)
@association_cache[name]
end
# Set the specified association instance.
def association_instance_set(name, association)
@association_cache[name] = association
end
# \Associations are a set of macro-like class methods for tying objects together through
# foreign keys. They express relationships like "Project has one Project Manager"
# or "Project belongs to a Portfolio". Each macro adds a number of methods to the
# class which are specialized according to the collection or association symbol and the
# options hash. It works much the same way as Ruby's own <tt>attr*</tt>
# methods.
#
# class Project < ActiveRecord::Base
# belongs_to :portfolio
# has_one :project_manager
# has_many :milestones
# has_and_belongs_to_many :categories
# end
#
# The project class now has the following methods (and more) to ease the traversal and
# manipulation of its relationships:
# * <tt>Project#portfolio, Project#portfolio=(portfolio), Project#portfolio.nil?</tt>
# * <tt>Project#project_manager, Project#project_manager=(project_manager), Project#project_manager.nil?,</tt>
# * <tt>Project#milestones.empty?, Project#milestones.size, Project#milestones, Project#milestones<<(milestone),</tt>
# <tt>Project#milestones.delete(milestone), Project#milestones.destroy(milestone), Project#milestones.find(milestone_id),</tt>
# <tt>Project#milestones.build, Project#milestones.create</tt>
# * <tt>Project#categories.empty?, Project#categories.size, Project#categories, Project#categories<<(category1),</tt>
# <tt>Project#categories.delete(category1), Project#categories.destroy(category1)</tt>
#
# === A word of warning
#
# Don't create associations that have the same name as instance methods of
# <tt>ActiveRecord::Base</tt>. Since the association adds a method with that name to
# its model, it will override the inherited method and break things.
# For instance, +attributes+ and +connection+ would be bad choices for association names.
#
# == Auto-generated methods
# See also Instance Public methods below for more details.
#
# === Singular associations (one-to-one)
# | | belongs_to |
# generated methods | belongs_to | :polymorphic | has_one
# ----------------------------------+------------+--------------+---------
# other(force_reload=false) | X | X | X
# other=(other) | X | X | X
# build_other(attributes={}) | X | | X
# create_other(attributes={}) | X | | X
# create_other!(attributes={}) | X | | X
#
# ===Collection associations (one-to-many / many-to-many)
# | | | has_many
# generated methods | habtm | has_many | :through
# ----------------------------------+-------+----------+----------
# others(force_reload=false) | X | X | X
# others=(other,other,...) | X | X | X
# other_ids | X | X | X
# other_ids=(id,id,...) | X | X | X
# others<< | X | X | X
# others.push | X | X | X
# others.concat | X | X | X
# others.build(attributes={}) | X | X | X
# others.create(attributes={}) | X | X | X
# others.create!(attributes={}) | X | X | X
# others.size | X | X | X
# others.length | X | X | X
# others.count | X | X | X
# others.sum(*args) | X | X | X
# others.empty? | X | X | X
# others.clear | X | X | X
# others.delete(other,other,...) | X | X | X
# others.delete_all | X | X | X
# others.destroy(other,other,...) | X | X | X
# others.destroy_all | X | X | X
# others.find(*args) | X | X | X
# others.exists? | X | X | X
# others.distinct | X | X | X
# others.uniq | X | X | X
# others.reset | X | X | X
#
# === Overriding generated methods
#
# Association methods are generated in a module that is included into the model class,
# which allows you to easily override with your own methods and call the original
# generated method with +super+. For example:
#
# class Car < ActiveRecord::Base
# belongs_to :owner
# belongs_to :old_owner
# def owner=(new_owner)
# self.old_owner = self.owner
# super
# end
# end
#
# If your model class is <tt>Project</tt>, the module is
# named <tt>Project::GeneratedFeatureMethods</tt>. The GeneratedFeatureMethods module is
# included in the model class immediately after the (anonymous) generated attributes methods
# module, meaning an association will override the methods for an attribute with the same name.
#
# == Cardinality and associations
#
# Active Record associations can be used to describe one-to-one, one-to-many and many-to-many
# relationships between models. Each model uses an association to describe its role in
# the relation. The +belongs_to+ association is always used in the model that has
# the foreign key.
#
# === One-to-one
#
# Use +has_one+ in the base, and +belongs_to+ in the associated model.
#
# class Employee < ActiveRecord::Base
# has_one :office
# end
# class Office < ActiveRecord::Base
# belongs_to :employee # foreign key - employee_id
# end
#
# === One-to-many
#
# Use +has_many+ in the base, and +belongs_to+ in the associated model.
#
# class Manager < ActiveRecord::Base
# has_many :employees
# end
# class Employee < ActiveRecord::Base
# belongs_to :manager # foreign key - manager_id
# end
#
# === Many-to-many
#
# There are two ways to build a many-to-many relationship.
#
# The first way uses a +has_many+ association with the <tt>:through</tt> option and a join model, so
# there are two stages of associations.
#
# class Assignment < ActiveRecord::Base
# belongs_to :programmer # foreign key - programmer_id
# belongs_to :project # foreign key - project_id
# end
# class Programmer < ActiveRecord::Base
# has_many :assignments
# has_many :projects, through: :assignments
# end
# class Project < ActiveRecord::Base
# has_many :assignments
# has_many :programmers, through: :assignments
# end
#
# For the second way, use +has_and_belongs_to_many+ in both models. This requires a join table
# that has no corresponding model or primary key.
#
# class Programmer < ActiveRecord::Base
# has_and_belongs_to_many :projects # foreign keys in the join table
# end
# class Project < ActiveRecord::Base
# has_and_belongs_to_many :programmers # foreign keys in the join table
# end
#
# Choosing which way to build a many-to-many relationship is not always simple.
# If you need to work with the relationship model as its own entity,
# use <tt>has_many :through</tt>. Use +has_and_belongs_to_many+ when working with legacy schemas or when
# you never work directly with the relationship itself.
#
# == Is it a +belongs_to+ or +has_one+ association?
#
# Both express a 1-1 relationship. The difference is mostly where to place the foreign
# key, which goes on the table for the class declaring the +belongs_to+ relationship.
#
# class User < ActiveRecord::Base
# # I reference an account.
# belongs_to :account
# end
#
# class Account < ActiveRecord::Base
# # One user references me.
# has_one :user
# end
#
# The tables for these classes could look something like:
#
# CREATE TABLE users (
# id int(11) NOT NULL auto_increment,
# account_id int(11) default NULL,
# name varchar default NULL,
# PRIMARY KEY (id)
# )
#
# CREATE TABLE accounts (
# id int(11) NOT NULL auto_increment,
# name varchar default NULL,
# PRIMARY KEY (id)
# )
#
# == Unsaved objects and associations
#
# You can manipulate objects and associations before they are saved to the database, but
# there is some special behavior you should be aware of, mostly involving the saving of
# associated objects.
#
# You can set the <tt>:autosave</tt> option on a <tt>has_one</tt>, <tt>belongs_to</tt>,
# <tt>has_many</tt>, or <tt>has_and_belongs_to_many</tt> association. Setting it
# to +true+ will _always_ save the members, whereas setting it to +false+ will
# _never_ save the members. More details about <tt>:autosave</tt> option is available at
# AutosaveAssociation.
#
# === One-to-one associations
#
# * Assigning an object to a +has_one+ association automatically saves that object and
# the object being replaced (if there is one), in order to update their foreign
# keys - except if the parent object is unsaved (<tt>new_record? == true</tt>).
# * If either of these saves fail (due to one of the objects being invalid), an
# <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is
# cancelled.
# * If you wish to assign an object to a +has_one+ association without saving it,
# use the <tt>build_association</tt> method (documented below). The object being
# replaced will still be saved to update its foreign key.
# * Assigning an object to a +belongs_to+ association does not save the object, since
# the foreign key field belongs on the parent. It does not save the parent either.
#
# === Collections
#
# * Adding an object to a collection (+has_many+ or +has_and_belongs_to_many+) automatically
# saves that object, except if the parent object (the owner of the collection) is not yet
# stored in the database.
# * If saving any of the objects being added to a collection (via <tt>push</tt> or similar)
# fails, then <tt>push</tt> returns +false+.
# * If saving fails while replacing the collection (via <tt>association=</tt>), an
# <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is
# cancelled.
# * You can add an object to a collection without automatically saving it by using the
# <tt>collection.build</tt> method (documented below).
# * All unsaved (<tt>new_record? == true</tt>) members of the collection are automatically
# saved when the parent is saved.
#
# == Customizing the query
#
# \Associations are built from <tt>Relation</tt>s, and you can use the <tt>Relation</tt> syntax
# to customize them. For example, to add a condition:
#
# class Blog < ActiveRecord::Base
# has_many :published_posts, -> { where published: true }, class_name: 'Post'
# end
#
# Inside the <tt>-> { ... }</tt> block you can use all of the usual <tt>Relation</tt> methods.
#
# === Accessing the owner object
#
# Sometimes it is useful to have access to the owner object when building the query. The owner
# is passed as a parameter to the block. For example, the following association would find all
# events that occur on the user's birthday:
#
# class User < ActiveRecord::Base
# has_many :birthday_events, ->(user) { where starts_on: user.birthday }, class_name: 'Event'
# end
#
# Note: Joining, eager loading and preloading of these associations is not fully possible.
# These operations happen before instance creation and the scope will be called with a +nil+ argument.
# This can lead to unexpected behavior and is deprecated.
#
# == Association callbacks
#
# Similar to the normal callbacks that hook into the life cycle of an Active Record object,
# you can also define callbacks that get triggered when you add an object to or remove an
# object from an association collection.
#
# class Project
# has_and_belongs_to_many :developers, after_add: :evaluate_velocity
#
# def evaluate_velocity(developer)
# ...
# end
# end
#
# It's possible to stack callbacks by passing them as an array. Example:
#
# class Project
# has_and_belongs_to_many :developers,
# after_add: [:evaluate_velocity, Proc.new { |p, d| p.shipping_date = Time.now}]
# end
#
# Possible callbacks are: +before_add+, +after_add+, +before_remove+ and +after_remove+.
#
# If any of the +before_add+ callbacks throw an exception, the object will not be
# added to the collection.
#
# Similarly, if any of the +before_remove+ callbacks throw an exception, the object
# will not be removed from the collection.
#
# == Association extensions
#
# The proxy objects that control the access to associations can be extended through anonymous
# modules. This is especially beneficial for adding new finders, creators, and other
# factory-type methods that are only used as part of this association.
#
# class Account < ActiveRecord::Base
# has_many :people do
# def find_or_create_by_name(name)
# first_name, last_name = name.split(" ", 2)
# find_or_create_by(first_name: first_name, last_name: last_name)
# end
# end
# end
#
# person = Account.first.people.find_or_create_by_name("David Heinemeier Hansson")
# person.first_name # => "David"
# person.last_name # => "Heinemeier Hansson"
#
# If you need to share the same extensions between many associations, you can use a named
# extension module.
#
# module FindOrCreateByNameExtension
# def find_or_create_by_name(name)
# first_name, last_name = name.split(" ", 2)
# find_or_create_by(first_name: first_name, last_name: last_name)
# end
# end
#
# class Account < ActiveRecord::Base
# has_many :people, -> { extending FindOrCreateByNameExtension }
# end
#
# class Company < ActiveRecord::Base
# has_many :people, -> { extending FindOrCreateByNameExtension }
# end
#
# Some extensions can only be made to work with knowledge of the association's internals.
# Extensions can access relevant state using the following methods (where +items+ is the
# name of the association):
#
# * <tt>record.association(:items).owner</tt> - Returns the object the association is part of.
# * <tt>record.association(:items).reflection</tt> - Returns the reflection object that describes the association.
# * <tt>record.association(:items).target</tt> - Returns the associated object for +belongs_to+ and +has_one+, or
# the collection of associated objects for +has_many+ and +has_and_belongs_to_many+.
#
# However, inside the actual extension code, you will not have access to the <tt>record</tt> as
# above. In this case, you can access <tt>proxy_association</tt>. For example,
# <tt>record.association(:items)</tt> and <tt>record.items.proxy_association</tt> will return
# the same object, allowing you to make calls like <tt>proxy_association.owner</tt> inside
# association extensions.
#
# == Association Join Models
#
# Has Many associations can be configured with the <tt>:through</tt> option to use an
# explicit join model to retrieve the data. This operates similarly to a
# +has_and_belongs_to_many+ association. The advantage is that you're able to add validations,
# callbacks, and extra attributes on the join model. Consider the following schema:
#
# class Author < ActiveRecord::Base
# has_many :authorships
# has_many :books, through: :authorships
# end
#
# class Authorship < ActiveRecord::Base
# belongs_to :author
# belongs_to :book
# end
#
# @author = Author.first
# @author.authorships.collect { |a| a.book } # selects all books that the author's authorships belong to
# @author.books # selects all books by using the Authorship join model
#
# You can also go through a +has_many+ association on the join model:
#
# class Firm < ActiveRecord::Base
# has_many :clients
# has_many :invoices, through: :clients
# end
#
# class Client < ActiveRecord::Base
# belongs_to :firm
# has_many :invoices
# end
#
# class Invoice < ActiveRecord::Base
# belongs_to :client
# end
#
# @firm = Firm.first
# @firm.clients.flat_map { |c| c.invoices } # select all invoices for all clients of the firm
# @firm.invoices # selects all invoices by going through the Client join model
#
# Similarly you can go through a +has_one+ association on the join model:
#
# class Group < ActiveRecord::Base
# has_many :users
# has_many :avatars, through: :users
# end
#
# class User < ActiveRecord::Base
# belongs_to :group
# has_one :avatar
# end
#
# class Avatar < ActiveRecord::Base
# belongs_to :user
# end
#
# @group = Group.first
# @group.users.collect { |u| u.avatar }.compact # select all avatars for all users in the group
# @group.avatars # selects all avatars by going through the User join model.
#
# An important caveat with going through +has_one+ or +has_many+ associations on the
# join model is that these associations are *read-only*. For example, the following
# would not work following the previous example:
#
# @group.avatars << Avatar.new # this would work if User belonged_to Avatar rather than the other way around
# @group.avatars.delete(@group.avatars.last) # so would this
#
# == Setting Inverses
#
# If you are using a +belongs_to+ on the join model, it is a good idea to set the
# <tt>:inverse_of</tt> option on the +belongs_to+, which will mean that the following example
# works correctly (where <tt>tags</tt> is a +has_many+ <tt>:through</tt> association):
#
# @post = Post.first
# @tag = @post.tags.build name: "ruby"
# @tag.save
#
# The last line ought to save the through record (a <tt>Taggable</tt>). This will only work if the
# <tt>:inverse_of</tt> is set:
#
# class Taggable < ActiveRecord::Base
# belongs_to :post
# belongs_to :tag, inverse_of: :taggings
# end
#
# If you do not set the <tt>:inverse_of</tt> record, the association will
# do its best to match itself up with the correct inverse. Automatic
# inverse detection only works on <tt>has_many</tt>, <tt>has_one</tt>, and
# <tt>belongs_to</tt> associations.
#
# Extra options on the associations, as defined in the
# <tt>AssociationReflection::INVALID_AUTOMATIC_INVERSE_OPTIONS</tt> constant, will
# also prevent the association's inverse from being found automatically.
#
# The automatic guessing of the inverse association uses a heuristic based
# on the name of the class, so it may not work for all associations,
# especially the ones with non-standard names.
#
# You can turn off the automatic detection of inverse associations by setting
# the <tt>:inverse_of</tt> option to <tt>false</tt> like so:
#
# class Taggable < ActiveRecord::Base
# belongs_to :tag, inverse_of: false
# end
#
# == Nested \Associations
#
# You can actually specify *any* association with the <tt>:through</tt> option, including an
# association which has a <tt>:through</tt> option itself. For example:
#
# class Author < ActiveRecord::Base
# has_many :posts
# has_many :comments, through: :posts
# has_many :commenters, through: :comments
# end
#
# class Post < ActiveRecord::Base
# has_many :comments
# end
#
# class Comment < ActiveRecord::Base
# belongs_to :commenter
# end
#
# @author = Author.first
# @author.commenters # => People who commented on posts written by the author
#
# An equivalent way of setting up this association this would be:
#
# class Author < ActiveRecord::Base
# has_many :posts
# has_many :commenters, through: :posts
# end
#
# class Post < ActiveRecord::Base
# has_many :comments
# has_many :commenters, through: :comments
# end
#
# class Comment < ActiveRecord::Base
# belongs_to :commenter
# end
#
# When using a nested association, you will not be able to modify the association because there
# is not enough information to know what modification to make. For example, if you tried to
# add a <tt>Commenter</tt> in the example above, there would be no way to tell how to set up the
# intermediate <tt>Post</tt> and <tt>Comment</tt> objects.
#
# == Polymorphic \Associations
#
# Polymorphic associations on models are not restricted on what types of models they
# can be associated with. Rather, they specify an interface that a +has_many+ association
# must adhere to.
#
# class Asset < ActiveRecord::Base
# belongs_to :attachable, polymorphic: true
# end
#
# class Post < ActiveRecord::Base
# has_many :assets, as: :attachable # The :as option specifies the polymorphic interface to use.
# end
#
# @asset.attachable = @post
#
# This works by using a type column in addition to a foreign key to specify the associated
# record. In the Asset example, you'd need an +attachable_id+ integer column and an
# +attachable_type+ string column.
#
# Using polymorphic associations in combination with single table inheritance (STI) is
# a little tricky. In order for the associations to work as expected, ensure that you
# store the base model for the STI models in the type column of the polymorphic
# association. To continue with the asset example above, suppose there are guest posts
# and member posts that use the posts table for STI. In this case, there must be a +type+
# column in the posts table.
#
# Note: The <tt>attachable_type=</tt> method is being called when assigning an +attachable+.
# The +class_name+ of the +attachable+ is passed as a String.
#
# class Asset < ActiveRecord::Base
# belongs_to :attachable, polymorphic: true
#
# def attachable_type=(class_name)
# super(class_name.constantize.base_class.to_s)
# end
# end
#
# class Post < ActiveRecord::Base
# # because we store "Post" in attachable_type now dependent: :destroy will work
# has_many :assets, as: :attachable, dependent: :destroy
# end
#
# class GuestPost < Post
# end
#
# class MemberPost < Post
# end
#
# == Caching
#
# All of the methods are built on a simple caching principle that will keep the result
# of the last query around unless specifically instructed not to. The cache is even
# shared across methods to make it even cheaper to use the macro-added methods without
# worrying too much about performance at the first go.
#
# project.milestones # fetches milestones from the database
# project.milestones.size # uses the milestone cache
# project.milestones.empty? # uses the milestone cache
# project.milestones(true).size # fetches milestones from the database
# project.milestones # uses the milestone cache
#
# == Eager loading of associations
#
# Eager loading is a way to find objects of a certain class and a number of named associations.
# It is one of the easiest ways to prevent the dreaded N+1 problem in which fetching 100
# posts that each need to display their author triggers 101 database queries. Through the
# use of eager loading, the number of queries will be reduced from 101 to 2.
#
# class Post < ActiveRecord::Base
# belongs_to :author
# has_many :comments
# end
#
# Consider the following loop using the class above:
#
# Post.all.each do |post|
# puts "Post: " + post.title
# puts "Written by: " + post.author.name
# puts "Last comment on: " + post.comments.first.created_on
# end
#
# To iterate over these one hundred posts, we'll generate 201 database queries. Let's
# first just optimize it for retrieving the author:
#
# Post.includes(:author).each do |post|
#
# This references the name of the +belongs_to+ association that also used the <tt>:author</tt>
# symbol. After loading the posts, find will collect the +author_id+ from each one and load
# all the referenced authors with one query. Doing so will cut down the number of queries
# from 201 to 102.
#
# We can improve upon the situation further by referencing both associations in the finder with:
#
# Post.includes(:author, :comments).each do |post|
#
# This will load all comments with a single query. This reduces the total number of queries
# to 3. In general, the number of queries will be 1 plus the number of associations
# named (except if some of the associations are polymorphic +belongs_to+ - see below).
#
# To include a deep hierarchy of associations, use a hash:
#
# Post.includes(:author, { comments: { author: :gravatar } }).each do |post|
#
# The above code will load all the comments and all of their associated
# authors and gravatars. You can mix and match any combination of symbols,
# arrays, and hashes to retrieve the associations you want to load.
#
# All of this power shouldn't fool you into thinking that you can pull out huge amounts
# of data with no performance penalty just because you've reduced the number of queries.
# The database still needs to send all the data to Active Record and it still needs to
# be processed. So it's no catch-all for performance problems, but it's a great way to
# cut down on the number of queries in a situation as the one described above.
#
# Since only one table is loaded at a time, conditions or orders cannot reference tables
# other than the main one. If this is the case, Active Record falls back to the previously
# used LEFT OUTER JOIN based strategy. For example:
#
# Post.includes([:author, :comments]).where(['comments.approved = ?', true])
#
# This will result in a single SQL query with joins along the lines of:
# <tt>LEFT OUTER JOIN comments ON comments.post_id = posts.id</tt> and
# <tt>LEFT OUTER JOIN authors ON authors.id = posts.author_id</tt>. Note that using conditions
# like this can have unintended consequences.
# In the above example posts with no approved comments are not returned at all, because
# the conditions apply to the SQL statement as a whole and not just to the association.
#
# You must disambiguate column references for this fallback to happen, for example
# <tt>order: "author.name DESC"</tt> will work but <tt>order: "name DESC"</tt> will not.
#
# If you want to load all posts (including posts with no approved comments) then write
# your own LEFT OUTER JOIN query using ON
#
# Post.joins("LEFT OUTER JOIN comments ON comments.post_id = posts.id AND comments.approved = '1'")
#
# In this case it is usually more natural to include an association which has conditions defined on it:
#
# class Post < ActiveRecord::Base
# has_many :approved_comments, -> { where approved: true }, class_name: 'Comment'
# end
#
# Post.includes(:approved_comments)
#
# This will load posts and eager load the +approved_comments+ association, which contains
# only those comments that have been approved.
#
# If you eager load an association with a specified <tt>:limit</tt> option, it will be ignored,
# returning all the associated objects:
#
# class Picture < ActiveRecord::Base
# has_many :most_recent_comments, -> { order('id DESC').limit(10) }, class_name: 'Comment'
# end
#
# Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments.
#
# Eager loading is supported with polymorphic associations.
#
# class Address < ActiveRecord::Base
# belongs_to :addressable, polymorphic: true
# end
#
# A call that tries to eager load the addressable model
#
# Address.includes(:addressable)
#
# This will execute one query to load the addresses and load the addressables with one
# query per addressable type.
# For example if all the addressables are either of class Person or Company then a total
# of 3 queries will be executed. The list of addressable types to load is determined on
# the back of the addresses loaded. This is not supported if Active Record has to fallback
# to the previous implementation of eager loading and will raise <tt>ActiveRecord::EagerLoadPolymorphicError</tt>.
# The reason is that the parent model's type is a column value so its corresponding table
# name cannot be put in the +FROM+/+JOIN+ clauses of that query.
#
# == Table Aliasing
#
# Active Record uses table aliasing in the case that a table is referenced multiple times
# in a join. If a table is referenced only once, the standard table name is used. The
# second time, the table is aliased as <tt>#{reflection_name}_#{parent_table_name}</tt>.
# Indexes are appended for any more successive uses of the table name.
#
# Post.joins(:comments)
# # => SELECT ... FROM posts INNER JOIN comments ON ...
# Post.joins(:special_comments) # STI
# # => SELECT ... FROM posts INNER JOIN comments ON ... AND comments.type = 'SpecialComment'
# Post.joins(:comments, :special_comments) # special_comments is the reflection name, posts is the parent table name
# # => SELECT ... FROM posts INNER JOIN comments ON ... INNER JOIN comments special_comments_posts
#
# Acts as tree example:
#
# TreeMixin.joins(:children)
# # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
# TreeMixin.joins(children: :parent)
# # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
# INNER JOIN parents_mixins ...
# TreeMixin.joins(children: {parent: :children})
# # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
# INNER JOIN parents_mixins ...
# INNER JOIN mixins childrens_mixins_2
#
# Has and Belongs to Many join tables use the same idea, but add a <tt>_join</tt> suffix:
#
# Post.joins(:categories)
# # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
# Post.joins(categories: :posts)
# # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
# INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
# Post.joins(categories: {posts: :categories})
# # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
# INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
# INNER JOIN categories_posts categories_posts_join INNER JOIN categories categories_posts_2
#
# If you wish to specify your own custom joins using <tt>joins</tt> method, those table
# names will take precedence over the eager associations:
#
# Post.joins(:comments).joins("inner join comments ...")
# # => SELECT ... FROM posts INNER JOIN comments_posts ON ... INNER JOIN comments ...
# Post.joins(:comments, :special_comments).joins("inner join comments ...")
# # => SELECT ... FROM posts INNER JOIN comments comments_posts ON ...
# INNER JOIN comments special_comments_posts ...
# INNER JOIN comments ...
#
# Table aliases are automatically truncated according to the maximum length of table identifiers
# according to the specific database.
#
# == Modules
#
# By default, associations will look for objects within the current module scope. Consider:
#
# module MyApplication
# module Business
# class Firm < ActiveRecord::Base
# has_many :clients
# end
#
# class Client < ActiveRecord::Base; end
# end
# end
#
# When <tt>Firm#clients</tt> is called, it will in turn call
# <tt>MyApplication::Business::Client.find_all_by_firm_id(firm.id)</tt>.
# If you want to associate with a class in another module scope, this can be done by
# specifying the complete class name.
#
# module MyApplication
# module Business
# class Firm < ActiveRecord::Base; end
# end
#
# module Billing
# class Account < ActiveRecord::Base
# belongs_to :firm, class_name: "MyApplication::Business::Firm"
# end
# end
# end
#
# == Bi-directional associations
#
# When you specify an association there is usually an association on the associated model
# that specifies the same relationship in reverse. For example, with the following models:
#
# class Dungeon < ActiveRecord::Base
# has_many :traps
# has_one :evil_wizard
# end
#
# class Trap < ActiveRecord::Base
# belongs_to :dungeon
# end
#
# class EvilWizard < ActiveRecord::Base
# belongs_to :dungeon
# end
#
# The +traps+ association on +Dungeon+ and the +dungeon+ association on +Trap+ are
# the inverse of each other and the inverse of the +dungeon+ association on +EvilWizard+
# is the +evil_wizard+ association on +Dungeon+ (and vice-versa). By default,
# Active Record doesn't know anything about these inverse relationships and so no object
# loading optimization is possible. For example:
#
# d = Dungeon.first
# t = d.traps.first
# d.level == t.dungeon.level # => true
# d.level = 10
# d.level == t.dungeon.level # => false
#
# The +Dungeon+ instances +d+ and <tt>t.dungeon</tt> in the above example refer to
# the same object data from the database, but are actually different in-memory copies
# of that data. Specifying the <tt>:inverse_of</tt> option on associations lets you tell
# Active Record about inverse relationships and it will optimise object loading. For
# example, if we changed our model definitions to:
#
# class Dungeon < ActiveRecord::Base
# has_many :traps, inverse_of: :dungeon
# has_one :evil_wizard, inverse_of: :dungeon
# end
#
# class Trap < ActiveRecord::Base
# belongs_to :dungeon, inverse_of: :traps
# end
#
# class EvilWizard < ActiveRecord::Base
# belongs_to :dungeon, inverse_of: :evil_wizard
# end
#
# Then, from our code snippet above, +d+ and <tt>t.dungeon</tt> are actually the same
# in-memory instance and our final <tt>d.level == t.dungeon.level</tt> will return +true+.
#
# There are limitations to <tt>:inverse_of</tt> support:
#
# * does not work with <tt>:through</tt> associations.
# * does not work with <tt>:polymorphic</tt> associations.
# * for +belongs_to+ associations +has_many+ inverse associations are ignored.
#
# == Deleting from associations
#
# === Dependent associations
#
# +has_many+, +has_one+ and +belongs_to+ associations support the <tt>:dependent</tt> option.
# This allows you to specify that associated records should be deleted when the owner is
# deleted.
#
# For example:
#
# class Author
# has_many :posts, dependent: :destroy
# end
# Author.find(1).destroy # => Will destroy all of the author's posts, too
#
# The <tt>:dependent</tt> option can have different values which specify how the deletion
# is done. For more information, see the documentation for this option on the different
# specific association types. When no option is given, the behavior is to do nothing
# with the associated records when destroying a record.
#
# Note that <tt>:dependent</tt> is implemented using Rails' callback
# system, which works by processing callbacks in order. Therefore, other
# callbacks declared either before or after the <tt>:dependent</tt> option
# can affect what it does.
#
# === Delete or destroy?
#
# +has_many+ and +has_and_belongs_to_many+ associations have the methods <tt>destroy</tt>,
# <tt>delete</tt>, <tt>destroy_all</tt> and <tt>delete_all</tt>.
#
# For +has_and_belongs_to_many+, <tt>delete</tt> and <tt>destroy</tt> are the same: they
# cause the records in the join table to be removed.
#
# For +has_many+, <tt>destroy</tt> and <tt>destroy_all</tt> will always call the <tt>destroy</tt> method of the
# record(s) being removed so that callbacks are run. However <tt>delete</tt> and <tt>delete_all</tt> will either
# do the deletion according to the strategy specified by the <tt>:dependent</tt> option, or
# if no <tt>:dependent</tt> option is given, then it will follow the default strategy.
# The default strategy is <tt>:nullify</tt> (set the foreign keys to <tt>nil</tt>), except for
# +has_many+ <tt>:through</tt>, where the default strategy is <tt>delete_all</tt> (delete
# the join records, without running their callbacks).
#
# There is also a <tt>clear</tt> method which is the same as <tt>delete_all</tt>, except that
# it returns the association rather than the records which have been deleted.
#
# === What gets deleted?
#
# There is a potential pitfall here: +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>
# associations have records in join tables, as well as the associated records. So when we
# call one of these deletion methods, what exactly should be deleted?
#
# The answer is that it is assumed that deletion on an association is about removing the
# <i>link</i> between the owner and the associated object(s), rather than necessarily the
# associated objects themselves. So with +has_and_belongs_to_many+ and +has_many+
# <tt>:through</tt>, the join records will be deleted, but the associated records won't.
#
# This makes sense if you think about it: if you were to call <tt>post.tags.delete(Tag.find_by(name: 'food'))</tt>
# you would want the 'food' tag to be unlinked from the post, rather than for the tag itself
# to be removed from the database.
#
# However, there are examples where this strategy doesn't make sense. For example, suppose
# a person has many projects, and each project has many tasks. If we deleted one of a person's
# tasks, we would probably not want the project to be deleted. In this scenario, the delete method
# won't actually work: it can only be used if the association on the join model is a
# +belongs_to+. In other situations you are expected to perform operations directly on
# either the associated records or the <tt>:through</tt> association.
#
# With a regular +has_many+ there is no distinction between the "associated records"
# and the "link", so there is only one choice for what gets deleted.
#
# With +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>, if you want to delete the
# associated records themselves, you can always do something along the lines of
# <tt>person.tasks.each(&:destroy)</tt>.
#
# == Type safety with <tt>ActiveRecord::AssociationTypeMismatch</tt>
#
# If you attempt to assign an object to an association that doesn't match the inferred
# or specified <tt>:class_name</tt>, you'll get an <tt>ActiveRecord::AssociationTypeMismatch</tt>.
#
# == Options
#
# All of the association macros can be specialized through options. This makes cases
# more complex than the simple and guessable ones possible.
module ClassMethods
# Specifies a one-to-many association. The following methods for retrieval and query of
# collections of associated objects will be added:
#
# +collection+ is a placeholder for the symbol passed as the +name+ argument, so
# <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.
#
# [collection(force_reload = false)]
# Returns an array of all the associated objects.
# An empty array is returned if none are found.
# [collection<<(object, ...)]
# Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
# Note that this operation instantly fires update SQL without waiting for the save or update call on the
# parent object, unless the parent object is a new record.
# [collection.delete(object, ...)]
# Removes one or more objects from the collection by setting their foreign keys to +NULL+.
# Objects will be in addition destroyed if they're associated with <tt>dependent: :destroy</tt>,
# and deleted if they're associated with <tt>dependent: :delete_all</tt>.
#
# If the <tt>:through</tt> option is used, then the join records are deleted (rather than
# nullified) by default, but you can specify <tt>dependent: :destroy</tt> or
# <tt>dependent: :nullify</tt> to override this.
# [collection.destroy(object, ...)]
# Removes one or more objects from the collection by running <tt>destroy</tt> on
# each record, regardless of any dependent option, ensuring callbacks are run.
#
# If the <tt>:through</tt> option is used, then the join records are destroyed
# instead, not the objects themselves.
# [collection=objects]
# Replaces the collections content by deleting and adding objects as appropriate. If the <tt>:through</tt>
# option is true callbacks in the join models are triggered except destroy callbacks, since deletion is
# direct.
# [collection_singular_ids]
# Returns an array of the associated objects' ids
# [collection_singular_ids=ids]
# Replace the collection with the objects identified by the primary keys in +ids+. This
# method loads the models and calls <tt>collection=</tt>. See above.
# [collection.clear]
# Removes every object from the collection. This destroys the associated objects if they
# are associated with <tt>dependent: :destroy</tt>, deletes them directly from the
# database if <tt>dependent: :delete_all</tt>, otherwise sets their foreign keys to +NULL+.
# If the <tt>:through</tt> option is true no destroy callbacks are invoked on the join models.
# Join models are directly deleted.
# [collection.empty?]
# Returns +true+ if there are no associated objects.
# [collection.size]
# Returns the number of associated objects.
# [collection.find(...)]
# Finds an associated object according to the same rules as <tt>ActiveRecord::Base.find</tt>.
# [collection.exists?(...)]
# Checks whether an associated object with the given conditions exists.
# Uses the same rules as <tt>ActiveRecord::Base.exists?</tt>.
# [collection.build(attributes = {}, ...)]
# Returns one or more new objects of the collection type that have been instantiated
# with +attributes+ and linked to this object through a foreign key, but have not yet
# been saved.
# [collection.create(attributes = {})]
# Returns a new object of the collection type that has been instantiated
# with +attributes+, linked to this object through a foreign key, and that has already
# been saved (if it passed the validation). *Note*: This only works if the base model
# already exists in the DB, not if it is a new (unsaved) record!
# [collection.create!(attributes = {})]
# Does the same as <tt>collection.create</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
# if the record is invalid.
#
# === Example
#
# A <tt>Firm</tt> class declares <tt>has_many :clients</tt>, which will add:
# * <tt>Firm#clients</tt> (similar to <tt>Client.where(firm_id: id)</tt>)
# * <tt>Firm#clients<<</tt>
# * <tt>Firm#clients.delete</tt>
# * <tt>Firm#clients.destroy</tt>
# * <tt>Firm#clients=</tt>
# * <tt>Firm#client_ids</tt>
# * <tt>Firm#client_ids=</tt>
# * <tt>Firm#clients.clear</tt>
# * <tt>Firm#clients.empty?</tt> (similar to <tt>firm.clients.size == 0</tt>)
# * <tt>Firm#clients.size</tt> (similar to <tt>Client.count "firm_id = #{id}"</tt>)
# * <tt>Firm#clients.find</tt> (similar to <tt>Client.where(firm_id: id).find(id)</tt>)
# * <tt>Firm#clients.exists?(name: 'ACME')</tt> (similar to <tt>Client.exists?(name: 'ACME', firm_id: firm.id)</tt>)
# * <tt>Firm#clients.build</tt> (similar to <tt>Client.new("firm_id" => id)</tt>)
# * <tt>Firm#clients.create</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save; c</tt>)
# * <tt>Firm#clients.create!</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save!</tt>)
# The declaration can also include an +options+ hash to specialize the behavior of the association.
#
# === Scopes
#
# You can pass a second argument +scope+ as a callable (i.e. proc or
# lambda) to retrieve a specific set of records or customize the generated
# query when you access the associated collection.
#
# Scope examples:
# has_many :comments, -> { where(author_id: 1) }
# has_many :employees, -> { joins(:address) }
# has_many :posts, ->(post) { where("max_post_length > ?", post.length) }
#
# === Extensions
#
# The +extension+ argument allows you to pass a block into a has_many
# association. This is useful for adding new finders, creators and other
# factory-type methods to be used as part of the association.
#
# Extension examples:
# has_many :employees do
# def find_or_create_by_name(name)
# first_name, last_name = name.split(" ", 2)
# find_or_create_by(first_name: first_name, last_name: last_name)
# end
# end
#
# === Options
# [:class_name]
# Specify the class name of the association. Use it only if that name can't be inferred
# from the association name. So <tt>has_many :products</tt> will by default be linked
# to the Product class, but if the real class name is SpecialProduct, you'll have to
# specify it with this option.
# [:foreign_key]
# Specify the foreign key used for the association. By default this is guessed to be the name
# of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_many+
# association will use "person_id" as the default <tt>:foreign_key</tt>.
# [:primary_key]
# Specify the name of the column to use as the primary key for the association. By default this is +id+.
# [:dependent]
# Controls what happens to the associated objects when
# their owner is destroyed. Note that these are implemented as
# callbacks, and Rails executes callbacks in order. Therefore, other
# similar callbacks may affect the <tt>:dependent</tt> behavior, and the
# <tt>:dependent</tt> behavior may affect other callbacks.
#
# * <tt>:destroy</tt> causes all the associated objects to also be destroyed.
# * <tt>:delete_all</tt> causes all the associated objects to be deleted directly from the database (so callbacks will not be executed).
# * <tt>:nullify</tt> causes the foreign keys to be set to +NULL+. Callbacks are not executed.
# * <tt>:restrict_with_exception</tt> causes an exception to be raised if there are any associated records.
# * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there are any associated objects.
#
# If using with the <tt>:through</tt> option, the association on the join model must be
# a +belongs_to+, and the records which get deleted are the join records, rather than
# the associated records.
# [:counter_cache]
# This option can be used to configure a custom named <tt>:counter_cache.</tt> You only need this option,
# when you customized the name of your <tt>:counter_cache</tt> on the <tt>belongs_to</tt> association.
# [:as]
# Specifies a polymorphic interface (See <tt>belongs_to</tt>).
# [:through]
# Specifies an association through which to perform the query. This can be any other type
# of association, including other <tt>:through</tt> associations. Options for <tt>:class_name</tt>,
# <tt>:primary_key</tt> and <tt>:foreign_key</tt> are ignored, as the association uses the
# source reflection.
#
# If the association on the join model is a +belongs_to+, the collection can be modified
# and the records on the <tt>:through</tt> model will be automatically created and removed
# as appropriate. Otherwise, the collection is read-only, so you should manipulate the
# <tt>:through</tt> association directly.
#
# If you are going to modify the association (rather than just read from it), then it is
# a good idea to set the <tt>:inverse_of</tt> option on the source association on the
# join model. This allows associated records to be built which will automatically create
# the appropriate join model records when they are saved. (See the 'Association Join Models'
# section above.)
# [:source]
# Specifies the source association name used by <tt>has_many :through</tt> queries.
# Only use it if the name cannot be inferred from the association.
# <tt>has_many :subscribers, through: :subscriptions</tt> will look for either <tt>:subscribers</tt> or
# <tt>:subscriber</tt> on Subscription, unless a <tt>:source</tt> is given.
# [:source_type]
# Specifies type of the source association used by <tt>has_many :through</tt> queries where the source
# association is a polymorphic +belongs_to+.
# [:validate]
# If +false+, don't validate the associated objects when saving the parent object. true by default.
# [:autosave]
# If true, always save the associated objects or destroy them if marked for destruction,
# when saving the parent object. If false, never save or destroy the associated objects.
# By default, only save associated objects that are new records. This option is implemented as a
# +before_save+ callback. Because callbacks are run in the order they are defined, associated objects
# may need to be explicitly saved in any user-defined +before_save+ callbacks.
#
# Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
# [:inverse_of]
# Specifies the name of the <tt>belongs_to</tt> association on the associated object
# that is the inverse of this <tt>has_many</tt> association. Does not work in combination
# with <tt>:through</tt> or <tt>:as</tt> options.
# See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
#
# Option examples:
# has_many :comments, -> { order "posted_on" }
# has_many :comments, -> { includes :author }
# has_many :people, -> { where(deleted: false).order("name") }, class_name: "Person"
# has_many :tracks, -> { order "position" }, dependent: :destroy
# has_many :comments, dependent: :nullify
# has_many :tags, as: :taggable
# has_many :reports, -> { readonly }
# has_many :subscribers, through: :subscriptions, source: :user
def has_many(name, scope = nil, options = {}, &extension)
reflection = Builder::HasMany.build(self, name, scope, options, &extension)
Reflection.add_reflection self, name, reflection
end
# Specifies a one-to-one association with another class. This method should only be used
# if the other class contains the foreign key. If the current class contains the foreign key,
# then you should use +belongs_to+ instead. See also ActiveRecord::Associations::ClassMethods's overview
# on when to use +has_one+ and when to use +belongs_to+.
#
# The following methods for retrieval and query of a single associated object will be added:
#
# +association+ is a placeholder for the symbol passed as the +name+ argument, so
# <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.
#
# [association(force_reload = false)]
# Returns the associated object. +nil+ is returned if none is found.
# [association=(associate)]
# Assigns the associate object, extracts the primary key, sets it as the foreign key,
# and saves the associate object. To avoid database inconsistencies, permanently deletes an existing
# associated object when assigning a new one, even if the new one isn't saved to database.
# [build_association(attributes = {})]
# Returns a new object of the associated type that has been instantiated
# with +attributes+ and linked to this object through a foreign key, but has not
# yet been saved.
# [create_association(attributes = {})]
# Returns a new object of the associated type that has been instantiated
# with +attributes+, linked to this object through a foreign key, and that
# has already been saved (if it passed the validation).
# [create_association!(attributes = {})]
# Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
# if the record is invalid.
#
# === Example
#
# An Account class declares <tt>has_one :beneficiary</tt>, which will add:
# * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.where(account_id: id).first</tt>)
# * <tt>Account#beneficiary=(beneficiary)</tt> (similar to <tt>beneficiary.account_id = account.id; beneficiary.save</tt>)
# * <tt>Account#build_beneficiary</tt> (similar to <tt>Beneficiary.new("account_id" => id)</tt>)
# * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save; b</tt>)
# * <tt>Account#create_beneficiary!</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save!; b</tt>)
#
# === Scopes
#
# You can pass a second argument +scope+ as a callable (i.e. proc or
# lambda) to retrieve a specific record or customize the generated query
# when you access the associated object.
#
# Scope examples:
# has_one :author, -> { where(comment_id: 1) }
# has_one :employer, -> { joins(:company) }
# has_one :dob, ->(dob) { where("Date.new(2000, 01, 01) > ?", dob) }
#
# === Options
#
# The declaration can also include an +options+ hash to specialize the behavior of the association.
#
# Options are:
# [:class_name]
# Specify the class name of the association. Use it only if that name can't be inferred
# from the association name. So <tt>has_one :manager</tt> will by default be linked to the Manager class, but
# if the real class name is Person, you'll have to specify it with this option.
# [:dependent]
# Controls what happens to the associated object when
# its owner is destroyed:
#
# * <tt>:destroy</tt> causes the associated object to also be destroyed
# * <tt>:delete</tt> causes the associated object to be deleted directly from the database (so callbacks will not execute)
# * <tt>:nullify</tt> causes the foreign key to be set to +NULL+. Callbacks are not executed.
# * <tt>:restrict_with_exception</tt> causes an exception to be raised if there is an associated record
# * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there is an associated object
# [:foreign_key]
# Specify the foreign key used for the association. By default this is guessed to be the name
# of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_one+ association
# will use "person_id" as the default <tt>:foreign_key</tt>.
# [:primary_key]
# Specify the method that returns the primary key used for the association. By default this is +id+.
# [:as]
# Specifies a polymorphic interface (See <tt>belongs_to</tt>).
# [:through]
# Specifies a Join Model through which to perform the query. Options for <tt>:class_name</tt>,
# <tt>:primary_key</tt>, and <tt>:foreign_key</tt> are ignored, as the association uses the
# source reflection. You can only use a <tt>:through</tt> query through a <tt>has_one</tt>
# or <tt>belongs_to</tt> association on the join model.
# [:source]
# Specifies the source association name used by <tt>has_one :through</tt> queries.
# Only use it if the name cannot be inferred from the association.
# <tt>has_one :favorite, through: :favorites</tt> will look for a
# <tt>:favorite</tt> on Favorite, unless a <tt>:source</tt> is given.
# [:source_type]
# Specifies type of the source association used by <tt>has_one :through</tt> queries where the source
# association is a polymorphic +belongs_to+.
# [:validate]
# If +false+, don't validate the associated object when saving the parent object. +false+ by default.
# [:autosave]
# If true, always save the associated object or destroy it if marked for destruction,
# when saving the parent object. If false, never save or destroy the associated object.
# By default, only save the associated object if it's a new record.
#
# Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
# [:inverse_of]
# Specifies the name of the <tt>belongs_to</tt> association on the associated object
# that is the inverse of this <tt>has_one</tt> association. Does not work in combination
# with <tt>:through</tt> or <tt>:as</tt> options.
# See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
# [:required]
# When set to +true+, the association will also have its presence validated.
# This will validate the association itself, not the id. You can use
# +:inverse_of+ to avoid an extra query during validation.
#
# Option examples:
# has_one :credit_card, dependent: :destroy # destroys the associated credit card
# has_one :credit_card, dependent: :nullify # updates the associated records foreign
# # key value to NULL rather than destroying it
# has_one :last_comment, -> { order 'posted_on' }, class_name: "Comment"
# has_one :project_manager, -> { where role: 'project_manager' }, class_name: "Person"
# has_one :attachment, as: :attachable
# has_one :boss, readonly: :true
# has_one :club, through: :membership
# has_one :primary_address, -> { where primary: true }, through: :addressables, source: :addressable
# has_one :credit_card, required: true
def has_one(name, scope = nil, options = {})
reflection = Builder::HasOne.build(self, name, scope, options)
Reflection.add_reflection self, name, reflection
end
# Specifies a one-to-one association with another class. This method should only be used
# if this class contains the foreign key. If the other class contains the foreign key,
# then you should use +has_one+ instead. See also ActiveRecord::Associations::ClassMethods's overview
# on when to use +has_one+ and when to use +belongs_to+.
#
# Methods will be added for retrieval and query for a single associated object, for which
# this object holds an id:
#
# +association+ is a placeholder for the symbol passed as the +name+ argument, so
# <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.
#
# [association(force_reload = false)]
# Returns the associated object. +nil+ is returned if none is found.
# [association=(associate)]
# Assigns the associate object, extracts the primary key, and sets it as the foreign key.
# [build_association(attributes = {})]
# Returns a new object of the associated type that has been instantiated
# with +attributes+ and linked to this object through a foreign key, but has not yet been saved.
# [create_association(attributes = {})]
# Returns a new object of the associated type that has been instantiated
# with +attributes+, linked to this object through a foreign key, and that
# has already been saved (if it passed the validation).
# [create_association!(attributes = {})]
# Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
# if the record is invalid.
#
# === Example
#
# A Post class declares <tt>belongs_to :author</tt>, which will add:
# * <tt>Post#author</tt> (similar to <tt>Author.find(author_id)</tt>)
# * <tt>Post#author=(author)</tt> (similar to <tt>post.author_id = author.id</tt>)
# * <tt>Post#build_author</tt> (similar to <tt>post.author = Author.new</tt>)
# * <tt>Post#create_author</tt> (similar to <tt>post.author = Author.new; post.author.save; post.author</tt>)
# * <tt>Post#create_author!</tt> (similar to <tt>post.author = Author.new; post.author.save!; post.author</tt>)
# The declaration can also include an +options+ hash to specialize the behavior of the association.
#
# === Scopes
#
# You can pass a second argument +scope+ as a callable (i.e. proc or
# lambda) to retrieve a specific record or customize the generated query
# when you access the associated object.
#
# Scope examples:
# belongs_to :user, -> { where(id: 2) }
# belongs_to :user, -> { joins(:friends) }
# belongs_to :level, ->(level) { where("game_level > ?", level.current) }
#
# === Options
#
# [:class_name]
# Specify the class name of the association. Use it only if that name can't be inferred
# from the association name. So <tt>belongs_to :author</tt> will by default be linked to the Author class, but
# if the real class name is Person, you'll have to specify it with this option.
# [:foreign_key]
# Specify the foreign key used for the association. By default this is guessed to be the name
# of the association with an "_id" suffix. So a class that defines a <tt>belongs_to :person</tt>
# association will use "person_id" as the default <tt>:foreign_key</tt>. Similarly,
# <tt>belongs_to :favorite_person, class_name: "Person"</tt> will use a foreign key
# of "favorite_person_id".
# [:foreign_type]
# Specify the column used to store the associated object's type, if this is a polymorphic
# association. By default this is guessed to be the name of the association with a "_type"
# suffix. So a class that defines a <tt>belongs_to :taggable, polymorphic: true</tt>
# association will use "taggable_type" as the default <tt>:foreign_type</tt>.
# [:primary_key]
# Specify the method that returns the primary key of associated object used for the association.
# By default this is id.
# [:dependent]
# If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
# <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method.
# This option should not be specified when <tt>belongs_to</tt> is used in conjunction with
# a <tt>has_many</tt> relationship on another class because of the potential to leave
# orphaned records behind.
# [:counter_cache]
# Caches the number of belonging objects on the associate class through the use of +increment_counter+
# and +decrement_counter+. The counter cache is incremented when an object of this
# class is created and decremented when it's destroyed. This requires that a column
# named <tt>#{table_name}_count</tt> (such as +comments_count+ for a belonging Comment class)
# is used on the associate class (such as a Post class) - that is the migration for
# <tt>#{table_name}_count</tt> is created on the associate class (such that <tt>Post.comments_count</tt> will
# return the count cached, see note below). You can also specify a custom counter
# cache column by providing a column name instead of a +true+/+false+ value to this
# option (e.g., <tt>counter_cache: :my_custom_counter</tt>.)
# Note: Specifying a counter cache will add it to that model's list of readonly attributes
# using +attr_readonly+.
# [:polymorphic]
# Specify this association is a polymorphic association by passing +true+.
# Note: If you've enabled the counter cache, then you may want to add the counter cache attribute
# to the +attr_readonly+ list in the associated classes (e.g. <tt>class Post; attr_readonly :comments_count; end</tt>).
# [:validate]
# If +false+, don't validate the associated objects when saving the parent object. +false+ by default.
# [:autosave]
# If true, always save the associated object or destroy it if marked for destruction, when
# saving the parent object.
# If false, never save or destroy the associated object.
# By default, only save the associated object if it's a new record.
#
# Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
# [:touch]
# If true, the associated object will be touched (the updated_at/on attributes set to current time)
# when this record is either saved or destroyed. If you specify a symbol, that attribute
# will be updated with the current time in addition to the updated_at/on attribute.
# [:inverse_of]
# Specifies the name of the <tt>has_one</tt> or <tt>has_many</tt> association on the associated
# object that is the inverse of this <tt>belongs_to</tt> association. Does not work in
# combination with the <tt>:polymorphic</tt> options.
# See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
# [:required]
# When set to +true+, the association will also have its presence validated.
# This will validate the association itself, not the id. You can use
# +:inverse_of+ to avoid an extra query during validation.
#
# Option examples:
# belongs_to :firm, foreign_key: "client_of"
# belongs_to :person, primary_key: "name", foreign_key: "person_name"
# belongs_to :author, class_name: "Person", foreign_key: "author_id"
# belongs_to :valid_coupon, ->(o) { where "discounts > ?", o.payments_count },
# class_name: "Coupon", foreign_key: "coupon_id"
# belongs_to :attachable, polymorphic: true
# belongs_to :project, readonly: true
# belongs_to :post, counter_cache: true
# belongs_to :company, touch: true
# belongs_to :company, touch: :employees_last_updated_at
# belongs_to :company, required: true
def belongs_to(name, scope = nil, options = {})
reflection = Builder::BelongsTo.build(self, name, scope, options)
Reflection.add_reflection self, name, reflection
end
# Specifies a many-to-many relationship with another class. This associates two classes via an
# intermediate join table. Unless the join table is explicitly specified as an option, it is
# guessed using the lexical order of the class names. So a join between Developer and Project
# will give the default join table name of "developers_projects" because "D" precedes "P" alphabetically.
# Note that this precedence is calculated using the <tt><</tt> operator for String. This
# means that if the strings are of different lengths, and the strings are equal when compared
# up to the shortest length, then the longer string is considered of higher
# lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers"
# to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes",
# but it in fact generates a join table name of "paper_boxes_papers". Be aware of this caveat, and use the
# custom <tt>:join_table</tt> option if you need to.
# If your tables share a common prefix, it will only appear once at the beginning. For example,
# the tables "catalog_categories" and "catalog_products" generate a join table name of "catalog_categories_products".
#
# The join table should not have a primary key or a model associated with it. You must manually generate the
# join table with a migration such as this:
#
# class CreateDevelopersProjectsJoinTable < ActiveRecord::Migration
# def change
# create_table :developers_projects, id: false do |t|
# t.integer :developer_id
# t.integer :project_id
# end
# end
# end
#
# It's also a good idea to add indexes to each of those columns to speed up the joins process.
# However, in MySQL it is advised to add a compound index for both of the columns as MySQL only
# uses one index per table during the lookup.
#
# Adds the following methods for retrieval and query:
#
# +collection+ is a placeholder for the symbol passed as the +name+ argument, so
# <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.
#
# [collection(force_reload = false)]
# Returns an array of all the associated objects.
# An empty array is returned if none are found.
# [collection<<(object, ...)]
# Adds one or more objects to the collection by creating associations in the join table
# (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method).
# Note that this operation instantly fires update SQL without waiting for the save or update call on the
# parent object, unless the parent object is a new record.
# [collection.delete(object, ...)]
# Removes one or more objects from the collection by removing their associations from the join table.
# This does not destroy the objects.
# [collection.destroy(object, ...)]
# Removes one or more objects from the collection by running destroy on each association in the join table, overriding any dependent option.
# This does not destroy the objects.
# [collection=objects]
# Replaces the collection's content by deleting and adding objects as appropriate.
# [collection_singular_ids]
# Returns an array of the associated objects' ids.
# [collection_singular_ids=ids]
# Replace the collection by the objects identified by the primary keys in +ids+.
# [collection.clear]
# Removes every object from the collection. This does not destroy the objects.
# [collection.empty?]
# Returns +true+ if there are no associated objects.
# [collection.size]
# Returns the number of associated objects.
# [collection.find(id)]
# Finds an associated object responding to the +id+ and that
# meets the condition that it has to be associated with this object.
# Uses the same rules as <tt>ActiveRecord::Base.find</tt>.
# [collection.exists?(...)]
# Checks whether an associated object with the given conditions exists.
# Uses the same rules as <tt>ActiveRecord::Base.exists?</tt>.
# [collection.build(attributes = {})]
# Returns a new object of the collection type that has been instantiated
# with +attributes+ and linked to this object through the join table, but has not yet been saved.
# [collection.create(attributes = {})]
# Returns a new object of the collection type that has been instantiated
# with +attributes+, linked to this object through the join table, and that has already been
# saved (if it passed the validation).
#
# === Example
#
# A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
# * <tt>Developer#projects</tt>
# * <tt>Developer#projects<<</tt>
# * <tt>Developer#projects.delete</tt>
# * <tt>Developer#projects.destroy</tt>
# * <tt>Developer#projects=</tt>
# * <tt>Developer#project_ids</tt>
# * <tt>Developer#project_ids=</tt>
# * <tt>Developer#projects.clear</tt>
# * <tt>Developer#projects.empty?</tt>
# * <tt>Developer#projects.size</tt>
# * <tt>Developer#projects.find(id)</tt>
# * <tt>Developer#projects.exists?(...)</tt>
# * <tt>Developer#projects.build</tt> (similar to <tt>Project.new("developer_id" => id)</tt>)
# * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("developer_id" => id); c.save; c</tt>)
# The declaration may include an +options+ hash to specialize the behavior of the association.
#
# === Scopes
#
# You can pass a second argument +scope+ as a callable (i.e. proc or
# lambda) to retrieve a specific set of records or customize the generated
# query when you access the associated collection.
#
# Scope examples:
# has_and_belongs_to_many :projects, -> { includes :milestones, :manager }
# has_and_belongs_to_many :categories, ->(category) {
# where("default_category = ?", category.name)
# }
#
# === Extensions
#
# The +extension+ argument allows you to pass a block into a
# has_and_belongs_to_many association. This is useful for adding new
# finders, creators and other factory-type methods to be used as part of
# the association.
#
# Extension examples:
# has_and_belongs_to_many :contractors do
# def find_or_create_by_name(name)
# first_name, last_name = name.split(" ", 2)
# find_or_create_by(first_name: first_name, last_name: last_name)
# end
# end
#
# === Options
#
# [:class_name]
# Specify the class name of the association. Use it only if that name can't be inferred
# from the association name. So <tt>has_and_belongs_to_many :projects</tt> will by default be linked to the
# Project class, but if the real class name is SuperProject, you'll have to specify it with this option.
# [:join_table]
# Specify the name of the join table if the default based on lexical order isn't what you want.
# <b>WARNING:</b> If you're overwriting the table name of either class, the +table_name+ method
# MUST be declared underneath any +has_and_belongs_to_many+ declaration in order to work.
# [:foreign_key]
# Specify the foreign key used for the association. By default this is guessed to be the name
# of this class in lower-case and "_id" suffixed. So a Person class that makes
# a +has_and_belongs_to_many+ association to Project will use "person_id" as the
# default <tt>:foreign_key</tt>.
# [:association_foreign_key]
# Specify the foreign key used for the association on the receiving side of the association.
# By default this is guessed to be the name of the associated class in lower-case and "_id" suffixed.
# So if a Person class makes a +has_and_belongs_to_many+ association to Project,
# the association will use "project_id" as the default <tt>:association_foreign_key</tt>.
# [:readonly]
# If true, all the associated objects are readonly through the association.
# [:validate]
# If +false+, don't validate the associated objects when saving the parent object. +true+ by default.
# [:autosave]
# If true, always save the associated objects or destroy them if marked for destruction, when
# saving the parent object.
# If false, never save or destroy the associated objects.
# By default, only save associated objects that are new records.
#
# Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
#
# Option examples:
# has_and_belongs_to_many :projects
# has_and_belongs_to_many :projects, -> { includes :milestones, :manager }
# has_and_belongs_to_many :nations, class_name: "Country"
# has_and_belongs_to_many :categories, join_table: "prods_cats"
# has_and_belongs_to_many :categories, -> { readonly }
def has_and_belongs_to_many(name, scope = nil, options = {}, &extension)
if scope.is_a?(Hash)
options = scope
scope = nil
end
habtm_reflection = ActiveRecord::Reflection::HasAndBelongsToManyReflection.new(name, scope, options, self)
builder = Builder::HasAndBelongsToMany.new name, self, options
join_model = builder.through_model
# FIXME: we should move this to the internal constants. Also people
# should never directly access this constant so I'm not happy about
# setting it.
const_set join_model.name, join_model
middle_reflection = builder.middle_reflection join_model
Builder::HasMany.define_callbacks self, middle_reflection
Reflection.add_reflection self, middle_reflection.name, middle_reflection
middle_reflection.parent_reflection = [name.to_s, habtm_reflection]
include Module.new {
class_eval <<-RUBY, __FILE__, __LINE__ + 1
def destroy_associations
association(:#{middle_reflection.name}).delete_all(:delete_all)
association(:#{name}).reset
super
end
RUBY
}
hm_options = {}
hm_options[:through] = middle_reflection.name
hm_options[:source] = join_model.right_reflection.name
[:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table].each do |k|
hm_options[k] = options[k] if options.key? k
end
has_many name, scope, hm_options, &extension
self._reflections[name.to_s].parent_reflection = [name.to_s, habtm_reflection]
end
end
end
end
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