332 lines
16 KiB
Ruby
332 lines
16 KiB
Ruby
require 'yaml'
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require 'set'
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require 'active_support/benchmarkable'
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require 'active_support/dependencies'
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require 'active_support/descendants_tracker'
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require 'active_support/time'
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require 'active_support/core_ext/class/attribute'
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require 'active_support/core_ext/class/attribute_accessors'
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require 'active_support/core_ext/class/delegating_attributes'
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require 'active_support/core_ext/array/extract_options'
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require 'active_support/core_ext/hash/deep_merge'
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require 'active_support/core_ext/hash/indifferent_access'
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require 'active_support/core_ext/hash/slice'
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require 'active_support/core_ext/string/behavior'
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require 'active_support/core_ext/kernel/singleton_class'
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require 'active_support/core_ext/module/delegation'
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require 'active_support/core_ext/module/introspection'
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require 'active_support/core_ext/object/duplicable'
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require 'active_support/core_ext/object/blank'
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require 'active_support/deprecation'
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require 'arel'
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require 'active_record/errors'
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require 'active_record/log_subscriber'
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require 'active_record/explain_subscriber'
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module ActiveRecord #:nodoc:
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# = Active Record
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#
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# Active Record objects don't specify their attributes directly, but rather infer them from
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# the table definition with which they're linked. Adding, removing, and changing attributes
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# and their type is done directly in the database. Any change is instantly reflected in the
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# Active Record objects. The mapping that binds a given Active Record class to a certain
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# database table will happen automatically in most common cases, but can be overwritten for the uncommon ones.
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#
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# See the mapping rules in table_name and the full example in link:files/activerecord/README_rdoc.html for more insight.
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#
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# == Creation
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#
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# Active Records accept constructor parameters either in a hash or as a block. The hash
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# method is especially useful when you're receiving the data from somewhere else, like an
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# HTTP request. It works like this:
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#
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# user = User.new(:name => "David", :occupation => "Code Artist")
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# user.name # => "David"
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#
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# You can also use block initialization:
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#
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# user = User.new do |u|
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# u.name = "David"
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# u.occupation = "Code Artist"
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# end
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#
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# And of course you can just create a bare object and specify the attributes after the fact:
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#
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# user = User.new
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# user.name = "David"
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# user.occupation = "Code Artist"
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#
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# == Conditions
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#
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# Conditions can either be specified as a string, array, or hash representing the WHERE-part of an SQL statement.
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# The array form is to be used when the condition input is tainted and requires sanitization. The string form can
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# be used for statements that don't involve tainted data. The hash form works much like the array form, except
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# only equality and range is possible. Examples:
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#
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# class User < ActiveRecord::Base
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# def self.authenticate_unsafely(user_name, password)
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# where("user_name = '#{user_name}' AND password = '#{password}'").first
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# end
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#
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# def self.authenticate_safely(user_name, password)
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# where("user_name = ? AND password = ?", user_name, password).first
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# end
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#
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# def self.authenticate_safely_simply(user_name, password)
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# where(:user_name => user_name, :password => password).first
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# end
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# end
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#
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# The <tt>authenticate_unsafely</tt> method inserts the parameters directly into the query
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# and is thus susceptible to SQL-injection attacks if the <tt>user_name</tt> and +password+
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# parameters come directly from an HTTP request. The <tt>authenticate_safely</tt> and
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# <tt>authenticate_safely_simply</tt> both will sanitize the <tt>user_name</tt> and +password+
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# before inserting them in the query, which will ensure that an attacker can't escape the
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# query and fake the login (or worse).
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#
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# When using multiple parameters in the conditions, it can easily become hard to read exactly
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# what the fourth or fifth question mark is supposed to represent. In those cases, you can
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# resort to named bind variables instead. That's done by replacing the question marks with
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# symbols and supplying a hash with values for the matching symbol keys:
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#
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# Company.where(
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# "id = :id AND name = :name AND division = :division AND created_at > :accounting_date",
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# { :id => 3, :name => "37signals", :division => "First", :accounting_date => '2005-01-01' }
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# ).first
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#
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# Similarly, a simple hash without a statement will generate conditions based on equality with the SQL AND
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# operator. For instance:
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#
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# Student.where(:first_name => "Harvey", :status => 1)
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# Student.where(params[:student])
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#
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# A range may be used in the hash to use the SQL BETWEEN operator:
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#
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# Student.where(:grade => 9..12)
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#
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# An array may be used in the hash to use the SQL IN operator:
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#
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# Student.where(:grade => [9,11,12])
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#
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# When joining tables, nested hashes or keys written in the form 'table_name.column_name'
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# can be used to qualify the table name of a particular condition. For instance:
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#
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# Student.joins(:schools).where(:schools => { :category => 'public' })
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# Student.joins(:schools).where('schools.category' => 'public' )
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#
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# == Overwriting default accessors
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#
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# All column values are automatically available through basic accessors on the Active Record
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# object, but sometimes you want to specialize this behavior. This can be done by overwriting
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# the default accessors (using the same name as the attribute) and calling
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# <tt>read_attribute(attr_name)</tt> and <tt>write_attribute(attr_name, value)</tt> to actually
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# change things.
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#
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# class Song < ActiveRecord::Base
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# # Uses an integer of seconds to hold the length of the song
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#
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# def length=(minutes)
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# write_attribute(:length, minutes.to_i * 60)
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# end
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#
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# def length
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# read_attribute(:length) / 60
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# end
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# end
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#
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# You can alternatively use <tt>self[:attribute]=(value)</tt> and <tt>self[:attribute]</tt>
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# instead of <tt>write_attribute(:attribute, value)</tt> and <tt>read_attribute(:attribute)</tt>.
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#
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# == Attribute query methods
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#
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# In addition to the basic accessors, query methods are also automatically available on the Active Record object.
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# Query methods allow you to test whether an attribute value is present.
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#
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# For example, an Active Record User with the <tt>name</tt> attribute has a <tt>name?</tt> method that you can call
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# to determine whether the user has a name:
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#
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# user = User.new(:name => "David")
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# user.name? # => true
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#
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# anonymous = User.new(:name => "")
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# anonymous.name? # => false
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#
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# == Accessing attributes before they have been typecasted
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#
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# Sometimes you want to be able to read the raw attribute data without having the column-determined
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# typecast run its course first. That can be done by using the <tt><attribute>_before_type_cast</tt>
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# accessors that all attributes have. For example, if your Account model has a <tt>balance</tt> attribute,
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# you can call <tt>account.balance_before_type_cast</tt> or <tt>account.id_before_type_cast</tt>.
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#
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# This is especially useful in validation situations where the user might supply a string for an
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# integer field and you want to display the original string back in an error message. Accessing the
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# attribute normally would typecast the string to 0, which isn't what you want.
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#
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# == Dynamic attribute-based finders
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#
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# Dynamic attribute-based finders are a cleaner way of getting (and/or creating) objects
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# by simple queries without turning to SQL. They work by appending the name of an attribute
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# to <tt>find_by_</tt>, <tt>find_last_by_</tt>, or <tt>find_all_by_</tt> and thus produces finders
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# like <tt>Person.find_by_user_name</tt>, <tt>Person.find_all_by_last_name</tt>, and
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# <tt>Payment.find_by_transaction_id</tt>. Instead of writing
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# <tt>Person.where(:user_name => user_name).first</tt>, you just do <tt>Person.find_by_user_name(user_name)</tt>.
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# And instead of writing <tt>Person.where(:last_name => last_name).all</tt>, you just do
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# <tt>Person.find_all_by_last_name(last_name)</tt>.
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#
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# It's possible to add an exclamation point (!) on the end of the dynamic finders to get them to raise an
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# <tt>ActiveRecord::RecordNotFound</tt> error if they do not return any records,
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# like <tt>Person.find_by_last_name!</tt>.
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#
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# It's also possible to use multiple attributes in the same find by separating them with "_and_".
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#
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# Person.where(:user_name => user_name, :password => password).first
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# Person.find_by_user_name_and_password(user_name, password) # with dynamic finder
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#
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# It's even possible to call these dynamic finder methods on relations and named scopes.
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#
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# Payment.order("created_on").find_all_by_amount(50)
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# Payment.pending.find_last_by_amount(100)
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#
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# The same dynamic finder style can be used to create the object if it doesn't already exist.
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# This dynamic finder is called with <tt>find_or_create_by_</tt> and will return the object if
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# it already exists and otherwise creates it, then returns it. Protected attributes won't be set
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# unless they are given in a block.
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#
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# # No 'Summer' tag exists
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# Tag.find_or_create_by_name("Summer") # equal to Tag.create(:name => "Summer")
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#
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# # Now the 'Summer' tag does exist
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# Tag.find_or_create_by_name("Summer") # equal to Tag.find_by_name("Summer")
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#
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# # Now 'Bob' exist and is an 'admin'
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# User.find_or_create_by_name('Bob', :age => 40) { |u| u.admin = true }
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#
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# Adding an exclamation point (!) on to the end of <tt>find_or_create_by_</tt> will
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# raise an <tt>ActiveRecord::RecordInvalid</tt> error if the new record is invalid.
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#
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# Use the <tt>find_or_initialize_by_</tt> finder if you want to return a new record without
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# saving it first. Protected attributes won't be set unless they are given in a block.
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#
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# # No 'Winter' tag exists
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# winter = Tag.find_or_initialize_by_name("Winter")
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# winter.persisted? # false
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#
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# To find by a subset of the attributes to be used for instantiating a new object, pass a hash instead of
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# a list of parameters.
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#
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# Tag.find_or_create_by_name(:name => "rails", :creator => current_user)
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#
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# That will either find an existing tag named "rails", or create a new one while setting the
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# user that created it.
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#
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# Just like <tt>find_by_*</tt>, you can also use <tt>scoped_by_*</tt> to retrieve data. The good thing about
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# using this feature is that the very first time result is returned using <tt>method_missing</tt> technique
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# but after that the method is declared on the class. Henceforth <tt>method_missing</tt> will not be hit.
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#
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# User.scoped_by_user_name('David')
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#
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# == Saving arrays, hashes, and other non-mappable objects in text columns
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#
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# Active Record can serialize any object in text columns using YAML. To do so, you must
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# specify this with a call to the class method +serialize+.
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# This makes it possible to store arrays, hashes, and other non-mappable objects without doing
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# any additional work.
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#
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# class User < ActiveRecord::Base
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# serialize :preferences
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# end
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#
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# user = User.create(:preferences => { "background" => "black", "display" => large })
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# User.find(user.id).preferences # => { "background" => "black", "display" => large }
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#
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# You can also specify a class option as the second parameter that'll raise an exception
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# if a serialized object is retrieved as a descendant of a class not in the hierarchy.
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#
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# class User < ActiveRecord::Base
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# serialize :preferences, Hash
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# end
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#
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# user = User.create(:preferences => %w( one two three ))
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# User.find(user.id).preferences # raises SerializationTypeMismatch
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#
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# When you specify a class option, the default value for that attribute will be a new
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# instance of that class.
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#
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# class User < ActiveRecord::Base
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# serialize :preferences, OpenStruct
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# end
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#
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# user = User.new
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# user.preferences.theme_color = "red"
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#
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#
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# == Single table inheritance
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#
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# Active Record allows inheritance by storing the name of the class in a column that by
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# default is named "type" (can be changed by overwriting <tt>Base.inheritance_column</tt>).
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# This means that an inheritance looking like this:
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#
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# class Company < ActiveRecord::Base; end
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# class Firm < Company; end
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# class Client < Company; end
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# class PriorityClient < Client; end
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#
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# When you do <tt>Firm.create(:name => "37signals")</tt>, this record will be saved in
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# the companies table with type = "Firm". You can then fetch this row again using
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# <tt>Company.where(:name => '37signals').first</tt> and it will return a Firm object.
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#
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# If you don't have a type column defined in your table, single-table inheritance won't
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# be triggered. In that case, it'll work just like normal subclasses with no special magic
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# for differentiating between them or reloading the right type with find.
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#
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# Note, all the attributes for all the cases are kept in the same table. Read more:
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# http://www.martinfowler.com/eaaCatalog/singleTableInheritance.html
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#
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# == Connection to multiple databases in different models
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#
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# Connections are usually created through ActiveRecord::Base.establish_connection and retrieved
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# by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this
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# connection. But you can also set a class-specific connection. For example, if Course is an
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# ActiveRecord::Base, but resides in a different database, you can just say <tt>Course.establish_connection</tt>
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# and Course and all of its subclasses will use this connection instead.
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#
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# This feature is implemented by keeping a connection pool in ActiveRecord::Base that is
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# a Hash indexed by the class. If a connection is requested, the retrieve_connection method
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# will go up the class-hierarchy until a connection is found in the connection pool.
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#
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# == Exceptions
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#
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# * ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
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# * AdapterNotSpecified - The configuration hash used in <tt>establish_connection</tt> didn't include an
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# <tt>:adapter</tt> key.
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# * AdapterNotFound - The <tt>:adapter</tt> key used in <tt>establish_connection</tt> specified a
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# non-existent adapter
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# (or a bad spelling of an existing one).
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# * AssociationTypeMismatch - The object assigned to the association wasn't of the type
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# specified in the association definition.
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# * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
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# * ConnectionNotEstablished+ - No connection has been established. Use <tt>establish_connection</tt>
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# before querying.
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# * RecordNotFound - No record responded to the +find+ method. Either the row with the given ID doesn't exist
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# or the row didn't meet the additional restrictions. Some +find+ calls do not raise this exception to signal
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# nothing was found, please check its documentation for further details.
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# * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
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# * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
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# <tt>attributes=</tt> method. The +errors+ property of this exception contains an array of
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# AttributeAssignmentError
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# objects that should be inspected to determine which attributes triggered the errors.
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# * AttributeAssignmentError - An error occurred while doing a mass assignment through the
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# <tt>attributes=</tt> method.
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# You can inspect the +attribute+ property of the exception object to determine which attribute
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# triggered the error.
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#
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# *Note*: The attributes listed are class-level attributes (accessible from both the class and instance level).
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# So it's possible to assign a logger to the class through <tt>Base.logger=</tt> which will then be used by all
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# instances in the current object space.
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class Base
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include ActiveRecord::Model
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end
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end
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ActiveSupport.run_load_hooks(:active_record, ActiveRecord::Model::DeprecationProxy)
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