# module ActiveRecord::AttributeMethods::ClassMethods

### Public Instance Methods

attribute_method?(attribute) click to toggle source

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

Calls superclass method

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

attribute_names() click to toggle source

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"]

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

column_for_attribute(name) click to toggle source

Returns the column object for the named attribute. Returns a `ActiveRecord::ConnectionAdapters::NullColumn` if the named attribute does not exist.

    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 lib/active_record/attribute_methods.rb, line 195
    def column_for_attribute(name)
      name = name.to_s
      columns_hash.fetch(name) do
        ConnectionAdapters::NullColumn.new(name)
      end
    end

dangerous_class_method?(method_name) click to toggle source

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.)

    # File 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

has_attribute?(attr_name) click to toggle source

Returns true if the given attribute exists, otherwise false.

    class Person < ActiveRecord::Base
    end

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

    # File lib/active_record/attribute_methods.rb, line 178
    def has_attribute?(attr_name)
      attribute_types.key?(attr_name.to_s)
    end

instance_method_already_implemented?(method_name) click to toggle source

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

Calls superclass method

    # File 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