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

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require 'active_support/core_ext/array/wrap'
require 'active_support/core_ext/enumerable'
require 'active_support/core_ext/module/delegation'
require 'active_support/core_ext/object/blank'
require 'active_support/core_ext/string/conversions'
require 'active_support/core_ext/module/remove_method'
require 'active_support/core_ext/class/attribute'
module ActiveRecord
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}'.")
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 HasManyThroughSourceAssociationNotFoundError < ActiveRecordError #:nodoc:
def initialize(reflection)
through_reflection = reflection.through_reflection
source_reflection_names = reflection.source_reflection_names
source_associations = reflection.through_reflection.klass.reflect_on_all_associations.collect { |a| a.name.inspect }
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 HasAndBelongsToManyAssociationForeignKeyNeeded < ActiveRecordError #:nodoc:
def initialize(reflection)
super("Cannot create self referential has_and_belongs_to_many association on '#{reflection.class_name rescue nil}##{reflection.name rescue nil}'. :association_foreign_key cannot be the same as the :foreign_key.")
end
end
class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
def initialize(reflection)
super("Can not eagerly load the polymorphic association #{reflection.name.inspect}")
end
end
class ReadOnlyAssociation < ActiveRecordError #:nodoc:
def initialize(reflection)
super("Can not 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::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 :HasAndBelongsToManyAssociation, 'active_record/associations/has_and_belongs_to_many_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
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'
autoload :JoinHelper, 'active_record/associations/join_helper'
# 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?
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.to_sym]
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.find(milestone_id), Project#milestones.all(options),</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)</tt>
#
# === 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.
#
# === 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
#
# === Singular associations (one-to-one)
# | | belongs_to |
# generated methods | belongs_to | :polymorphic | has_one
# ----------------------------------+------------+--------------+---------
# other | 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 | 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*,&block) | 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_all | X | X | X
# others.find(*args) | X | X | X
# others.exists? | X | X | X
# others.uniq | X | X | X
# others.reset | X | X | X
#
# == 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 :autosave 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 :autosave option is available at
# autosave_association.rb .
#
# === 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.
#
# === 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+.
#
# Should any of the +before_add+ callbacks throw an exception, the object does not get
# added to the collection. Same with the +before_remove+ callbacks; if an exception is
# thrown the object doesn't get removed.
#
# === 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_and_last_name(first_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_and_last_name(first_name, last_name)
# end
# end
#
# class Account < ActiveRecord::Base
# has_many :people, :extend => FindOrCreateByNameExtension
# end
#
# class Company < ActiveRecord::Base
# has_many :people, :extend => FindOrCreateByNameExtension
# end
#
# If you need to use multiple named extension modules, you can specify an array of modules
# with the <tt>:extend</tt> option.
# In the case of name conflicts between methods in the modules, methods in modules later
# in the array supercede those earlier in the array.
#
# class Account < ActiveRecord::Base
# has_many :people, :extend => [FindOrCreateByNameExtension, FindRecentExtension]
# 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.collect { |c| c.invoices }.flatten # 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 }.flatten # 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
#
# 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
#
# === 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 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.
#
# class Asset < ActiveRecord::Base
# belongs_to :attachable, :polymorphic => true
#
# def attachable_type=(sType)
# super(sType.to_s.classify.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.
# This is one of the easiest ways of to prevent the dreaded 1+N problem in which fetching 100
# posts that each need to display their author triggers 101 database queries. Through the
# use of eager loading, the 101 queries can be reduced 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. More generally 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|
#
# That'll grab not only all the comments but all their authors and gravatar pictures.
# You can mix and match symbols, arrays and hashes in any combination to describe 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]).all
#
# 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 do want eager load only some members of an association it is usually more natural
# to include an association which has conditions defined on it:
#
# class Post < ActiveRecord::Base
# has_many :approved_comments, :class_name => 'Comment', :conditions => ['approved = ?', true]
# 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, :class_name => 'Comment', :order => 'id DESC', :limit => 10
# end
#
# Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments.
#
# When eager loaded, conditions are interpolated in the context of the model class, not
# the model instance. Conditions are lazily interpolated before the actual model exists.
#
# 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 ActiveRecord::EagerLoadPolymorphicError.
# 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.
#
# === 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> will always call the <tt>destroy</tt> method of the
# record(s) being removed so that callbacks are run. However <tt>delete</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(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.
# [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=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 ActiveRecord::Base.find.
# [collection.exists?(...)]
# Checks whether an associated object with the given conditions exists.
# Uses the same rules as ActiveRecord::Base.exists?.
# [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!
#
# (*Note*: +collection+ is replaced with the symbol passed as the first argument, so
# <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.)
#
# === Example
#
# Example: A Firm class declares <tt>has_many :clients</tt>, which will add:
# * <tt>Firm#clients</tt> (similar to <tt>Clients.all :conditions => ["firm_id = ?", id]</tt>)
# * <tt>Firm#clients<<</tt>
# * <tt>Firm#clients.delete</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.find(id, :conditions => "firm_id = #{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>)
# The declaration can also include an options hash to specialize the behavior of the association.
#
# === 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.
# [:conditions]
# Specify the conditions that the associated objects must meet in order to be included as a +WHERE+
# SQL fragment, such as <tt>price > 5 AND name LIKE 'B%'</tt>. Record creations from
# the association are scoped if a hash is used.
# <tt>has_many :posts, :conditions => {:published => true}</tt> will create published
# posts with <tt>@blog.posts.create</tt> or <tt>@blog.posts.build</tt>.
# [:order]
# Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
# such as <tt>last_name, first_name DESC</tt>.
# [: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 method that returns the primary key used for the association. By default this is +id+.
# [:dependent]
# If set to <tt>:destroy</tt> all the associated objects are destroyed
# alongside this object by calling their +destroy+ method. If set to <tt>:delete_all</tt> all associated
# objects are deleted *without* calling their +destroy+ method. If set to <tt>:nullify</tt> all associated
# objects' foreign keys are set to +NULL+ *without* calling their +save+ callbacks. If set to
# <tt>:restrict</tt> this object raises an <tt>ActiveRecord::DeleteRestrictionError</tt> exception and
# cannot be deleted if it has 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.
#
# [:finder_sql]
# Specify a complete SQL statement to fetch the association. This is a good way to go for complex
# associations that depend on multiple tables. May be supplied as a string or a proc where interpolation is
# required. Note: When this option is used, +find_in_collection+
# is _not_ added.
# [:counter_sql]
# Specify a complete SQL statement to fetch the size of the association. If <tt>:finder_sql</tt> is
# specified but not <tt>:counter_sql</tt>, <tt>:counter_sql</tt> will be generated by
# replacing <tt>SELECT ... FROM</tt> with <tt>SELECT COUNT(*) FROM</tt>.
# [:extend]
# Specify a named module for extending the proxy. See "Association extensions".
# [:include]
# Specify second-order associations that should be eager loaded when the collection is loaded.
# [:group]
# An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
# [:having]
# Combined with +:group+ this can be used to filter the records that a <tt>GROUP BY</tt>
# returns. Uses the <tt>HAVING</tt> SQL-clause.
# [:limit]
# An integer determining the limit on the number of rows that should be returned.
# [:offset]
# An integer determining the offset from where the rows should be fetched. So at 5,
# it would skip the first 4 rows.
# [:select]
# By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if
# you, for example, want to do a join but not include the joined columns. Do not forget
# to include the primary and foreign keys, otherwise it will raise an error.
# [: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+.
# [:uniq]
# If true, duplicates will be omitted from the collection. Useful in conjunction with <tt>:through</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.
# [: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, :include => :author
# has_many :people, :class_name => "Person", :conditions => "deleted = 0", :order => "name"
# has_many :tracks, :order => "position", :dependent => :destroy
# has_many :comments, :dependent => :nullify
# has_many :tags, :as => :taggable
# has_many :reports, :readonly => true
# has_many :subscribers, :through => :subscriptions, :source => :user
# has_many :subscribers, :class_name => "Person", :finder_sql => Proc.new {
# %Q{
# SELECT DISTINCT *
# FROM people p, post_subscriptions ps
# WHERE ps.post_id = #{id} AND ps.person_id = p.id
# ORDER BY p.first_name
# }
# }
def has_many(name, options = {}, &extension)
Builder::HasMany.build(self, name, options, &extension)
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(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.
# [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.
#
# (+association+ is replaced with the symbol passed as the first argument, so
# <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.)
#
# === Example
#
# An Account class declares <tt>has_one :beneficiary</tt>, which will add:
# * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.first(:conditions => "account_id = #{id}")</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>)
#
# === 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.
# [:conditions]
# Specify the conditions that the associated object must meet in order to be included as a +WHERE+
# SQL fragment, such as <tt>rank = 5</tt>. Record creation from the association is scoped if a hash
# is used. <tt>has_one :account, :conditions => {:enabled => true}</tt> will create
# an enabled account with <tt>@company.create_account</tt> or <tt>@company.build_account</tt>.
# [:order]
# Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
# such as <tt>last_name, first_name DESC</tt>.
# [: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.
# If set to <tt>:nullify</tt>, the associated object's foreign key is set to +NULL+.
# Also, association is assigned. If set to <tt>:restrict</tt> this object raises an
# <tt>ActiveRecord::DeleteRestrictionError</tt> exception and cannot be deleted if it has any 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+.
# [:include]
# Specify second-order associations that should be eager loaded when this object is loaded.
# [:as]
# Specifies a polymorphic interface (See <tt>belongs_to</tt>).
# [:select]
# By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example,
# you want to do a join but not include the joined columns. Do not forget to include the
# primary and foreign keys, otherwise it will raise an error.
# [: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+.
# [:readonly]
# If true, the associated object is readonly through the association.
# [: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.
# [: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.
#
# 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, :class_name => "Comment", :order => "posted_on"
# has_one :project_manager, :class_name => "Person", :conditions => "role = 'project_manager'"
# has_one :attachment, :as => :attachable
# has_one :boss, :readonly => :true
# has_one :club, :through => :membership
# has_one :primary_address, :through => :addressables, :conditions => ["addressable.primary = ?", true], :source => :addressable
def has_one(name, options = {})
Builder::HasOne.build(self, name, options)
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(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.
#
# (+association+ is replaced with the symbol passed as the first argument, so
# <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.)
#
# === 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.
#
# === 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.
# [:conditions]
# Specify the conditions that the associated object must meet in order to be included as a +WHERE+
# SQL fragment, such as <tt>authorized = 1</tt>.
# [:select]
# By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed
# if, for example, you want to do a join but not include the joined columns. Do not
# forget to include the primary and foreign keys, otherwise it will raise an error.
# [: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). 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+.
# [:include]
# Specify second-order associations that should be eager loaded when this object is loaded.
# [: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>).
# [:readonly]
# If true, the associated object is readonly through the association.
# [: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.
# [:touch]
# If true, the associated object will be touched (the updated_at/on attributes set to now)
# 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.
#
# 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, :class_name => "Coupon", :foreign_key => "coupon_id",
# :conditions => 'discounts > #{payments_count}'
# 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
def belongs_to(name, options = {})
Builder::BelongsTo.build(self, name, options)
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" outranks "P".
# 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.
#
# 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(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.
# [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=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 ActiveRecord::Base.find.
# [collection.exists?(...)]
# Checks whether an associated object with the given conditions exists.
# Uses the same rules as ActiveRecord::Base.exists?.
# [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).
#
# (+collection+ is replaced with the symbol passed as the first argument, so
# <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.)
#
# === 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=</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("project_id" => id)</tt>)
# * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("project_id" => id); c.save; c</tt>)
# The declaration may include an options hash to specialize the behavior of the association.
#
# === 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>.
# [:conditions]
# Specify the conditions that the associated object must meet in order to be included as a +WHERE+
# SQL fragment, such as <tt>authorized = 1</tt>. Record creations from the association are
# scoped if a hash is used.
# <tt>has_many :posts, :conditions => {:published => true}</tt> will create published posts with <tt>@blog.posts.create</tt>
# or <tt>@blog.posts.build</tt>.
# [:order]
# Specify the order in which the associated objects are returned as an <tt>ORDER BY</tt> SQL fragment,
# such as <tt>last_name, first_name DESC</tt>
# [:uniq]
# If true, duplicate associated objects will be ignored by accessors and query methods.
# [:finder_sql]
# Overwrite the default generated SQL statement used to fetch the association with a manual statement
# [:counter_sql]
# Specify a complete SQL statement to fetch the size of the association. If <tt>:finder_sql</tt> is
# specified but not <tt>:counter_sql</tt>, <tt>:counter_sql</tt> will be generated by
# replacing <tt>SELECT ... FROM</tt> with <tt>SELECT COUNT(*) FROM</tt>.
# [:delete_sql]
# Overwrite the default generated SQL statement used to remove links between the associated
# classes with a manual statement.
# [:insert_sql]
# Overwrite the default generated SQL statement used to add links between the associated classes
# with a manual statement.
# [:extend]
# Anonymous module for extending the proxy, see "Association extensions".
# [:include]
# Specify second-order associations that should be eager loaded when the collection is loaded.
# [:group]
# An attribute name by which the result should be grouped. Uses the <tt>GROUP BY</tt> SQL-clause.
# [:having]
# Combined with +:group+ this can be used to filter the records that a <tt>GROUP BY</tt> returns.
# Uses the <tt>HAVING</tt> SQL-clause.
# [:limit]
# An integer determining the limit on the number of rows that should be returned.
# [:offset]
# An integer determining the offset from where the rows should be fetched. So at 5,
# it would skip the first 4 rows.
# [:select]
# By default, this is <tt>*</tt> as in <tt>SELECT * FROM</tt>, but can be changed if, for example,
# you want to do a join but not include the joined columns. Do not forget to include the primary
# and foreign keys, otherwise it will raise an error.
# [: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.
#
# Option examples:
# has_and_belongs_to_many :projects
# has_and_belongs_to_many :projects, :include => [ :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 => true
# has_and_belongs_to_many :active_projects, :join_table => 'developers_projects', :delete_sql =>
# "DELETE FROM developers_projects WHERE active=1 AND developer_id = #{id} AND project_id = #{record.id}"
def has_and_belongs_to_many(name, options = {}, &extension)
Builder::HasAndBelongsToMany.build(self, name, options, &extension)
end
end
end
end
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