модуль ActiveRecord::AttributeMethods::ClassMethods

# File activerecord/lib/active_record/attribute_methods.rb, line 150
def attribute_method?(attribute)
  super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, "")))
end

Возвращает true если attribute является методом атрибута и таблица существует, false в противном случае.

class Person < ActiveRecord::Base
end

Person.attribute_method?('name')   # => true
Person.attribute_method?(:age=)    # => true
Person.attribute_method?(:nothing) # => false

# File activerecord/lib/active_record/attribute_methods.rb, line 162
def attribute_names
  @attribute_names ||= if !abstract_class? && table_exists?
    attribute_types.keys
  else
    []
  end
end

Возвращает массив имён столбцов в виде строк, если это не абстрактный класс и таблица существует. В противном случае возвращает пустой массив.

class Person < ActiveRecord::Base
end

Person.attribute_names
# => ["id", "created_at", "updated_at", "name", "age"]

# File activerecord/lib/active_record/attribute_methods.rb, line 246
def column_for_attribute(name)
  name = name.to_s
  columns_hash.fetch(name) do
    ConnectionAdapters::NullColumn.new(name)
  end
end

Возвращает объект столбца для заданного атрибута. Возвращает ActiveRecord::ConnectionAdapters::NullColumn если заданный атрибут не существует.

class Person < ActiveRecord::Base
end

person = Person.new
person.column_for_attribute(:name) # the result depends on the ConnectionAdapter
# => #<ActiveRecord::ConnectionAdapters::Column:0x007ff4ab083980 @name="name", @sql_type="varchar(255)", @null=true, ...>

person.column_for_attribute(:nothing)
# => #<ActiveRecord::ConnectionAdapters::NullColumn:0xXXX @name=nil, @sql_type=nil, @cast_type=#<Type::Value>, ...>

# File activerecord/lib/active_record/attribute_methods.rb, line 125
def dangerous_class_method?(method_name)
  BLACKLISTED_CLASS_METHODS.include?(method_name.to_s) || class_method_defined_within?(method_name, Base)
end

Метод класса считается «опасным», если он уже (пере)определён Active Record, но не каким-либо предком. (Например, «puts» неопасен, а «new» — опасен.)

# File activerecord/lib/active_record/attribute_methods.rb, line 229
def has_attribute?(attr_name)
  attribute_types.key?(attr_name.to_s)
end

Возвращает true, если заданный атрибут существует, иначе false.

class Person < ActiveRecord::Base
end

Person.has_attribute?('name')   # => true
Person.has_attribute?(:age)     # => true
Person.has_attribute?(:nothing) # => false

# File activerecord/lib/active_record/attribute_methods.rb, line 89
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 overwrite that.
    defined = method_defined_within?(method_name, superclass, Base) &&
      ! superclass.instance_method(method_name).owner.is_a?(GeneratedAttributeMethods)
    defined || super
  end
end

Выбрасывает исключение ActiveRecord::DangerousAttributeError, если метод Active Record определён в модели, иначе 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