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module ActiveRecord::AttributeMethods::ClassMethods

Public instance methods

alias_attribute(new_name, old_name)

Allows you to make aliases for attributes.

class Person < ActiveRecord::Base
  alias_attribute :nickname, :name
end

person = Person.create(name: 'Bob')
person.name     # => "Bob"
person.nickname # => "Bob"

The alias can also be used for querying:

Person.where(nickname: "Bob")
# SELECT "people".* FROM "people" WHERE "people"."name" = "Bob"
Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 66
def alias_attribute(new_name, old_name)
  super

  if @alias_attributes_mass_generated
    ActiveSupport::CodeGenerator.batch(generated_attribute_methods, __FILE__, __LINE__) do |code_generator|
      generate_alias_attribute_methods(code_generator, new_name, old_name)
    end
  end
end

alias_attribute_method_definition(code_generator, pattern, new_name, old_name)

Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 80
def alias_attribute_method_definition(code_generator, pattern, new_name, old_name)
  old_name = old_name.to_s

  if !abstract_class? && !has_attribute?(old_name)
    raise ArgumentError, "#{self.name} model aliases `#{old_name}`, but `#{old_name}` is not an attribute. " \
      "Use `alias_method :#{new_name}, :#{old_name}` or define the method manually."
  else
    method_name = pattern.method_name(new_name).to_s
    parameters = pattern.parameters

    define_proxy_call(code_generator, method_name, pattern.proxy_target, parameters, old_name,
      namespace: :proxy_alias_attribute
    )
  end
end

attribute_method?(attribute)

Returns true if attribute is an attribute method and table exists, false otherwise.

class Person < ActiveRecord::Base
end

Person.attribute_method?('name')   # => true
Person.attribute_method?(:age=)    # => true
Person.attribute_method?(:nothing) # => false
Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 221
def attribute_method?(attribute)
  super || (table_exists? && column_names.include?(attribute.to_s.delete_suffix("=")))
end

attribute_names()

Returns an array of column names as strings if it’s not an abstract class and table exists. Otherwise it returns an empty array.

class Person < ActiveRecord::Base
end

Person.attribute_names
# => ["id", "created_at", "updated_at", "name", "age"]
Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 233
def attribute_names
  @attribute_names ||= if !abstract_class? && table_exists?
    attribute_types.keys
  else
    []
  end.freeze
end

dangerous_class_method?(method_name)

A class method is ‘dangerous’ if it is already (re)defined by Active Record, but not by any ancestors. (So ‘puts’ is not dangerous but ‘new’ is.)

Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 198
def dangerous_class_method?(method_name)
  return true if RESTRICTED_CLASS_METHODS.include?(method_name.to_s)

  if Base.respond_to?(method_name, true)
    if Object.respond_to?(method_name, true)
      Base.method(method_name).owner != Object.method(method_name).owner
    else
      true
    end
  else
    false
  end
end

has_attribute?(attr_name)

Returns true if the given attribute exists, otherwise false.

class Person < ActiveRecord::Base
  alias_attribute :new_name, :name
end

Person.has_attribute?('name')     # => true
Person.has_attribute?('new_name') # => true
Person.has_attribute?(:age)       # => true
Person.has_attribute?(:nothing)   # => false
Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 251
def has_attribute?(attr_name)
  attr_name = attr_name.to_s
  attr_name = attribute_aliases[attr_name] || attr_name
  attribute_types.key?(attr_name)
end

instance_method_already_implemented?(method_name)

Raises an ActiveRecord::DangerousAttributeError exception when an Active Record method is defined in the model, otherwise false.

class Person < ActiveRecord::Base
  def save
    'already defined by Active Record'
  end
end

Person.instance_method_already_implemented?(:save)
# => ActiveRecord::DangerousAttributeError: save is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name.

Person.instance_method_already_implemented?(:name)
# => false
Source code GitHub 
# File activerecord/lib/active_record/attribute_methods.rb, line 162
def instance_method_already_implemented?(method_name)
  if dangerous_attribute_method?(method_name)
    raise DangerousAttributeError, "#{method_name} is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name."
  end

  if superclass == Base
    super
  else
    # If ThisClass < ... < SomeSuperClass < ... < Base and SomeSuperClass
    # defines its own attribute method, then we don't want to override that.
    defined = method_defined_within?(method_name, superclass, Base) &&
      ! superclass.instance_method(method_name).owner.is_a?(GeneratedAttributeMethods)
    defined || super
  end
end

Definition files