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module ActiveRecord
# See ActiveRecord::Attributes::ClassMethods for documentation
module Attributes
extend ActiveSupport::Concern
# :nodoc:
Type = ActiveRecord::Type
included do
class_attribute :attributes_to_define_after_schema_loads, instance_accessor: false # :internal:
self.attributes_to_define_after_schema_loads = {}
end
module ClassMethods
# Defines an attribute with a type on this model. It will override the
# type of existing attributes if needed. This allows control over how
# values are converted to and from SQL when assigned to a model. It also
# changes the behavior of values passed to
# ActiveRecord::QueryMethods#where. This will let you use
# your domain objects across much of Active Record, without having to
# rely on implementation details or monkey patching.
#
# +name+ The name of the methods to define attribute methods for, and the
# column which this will persist to.
#
# +cast_type+ A symbol such as +:string+ or +:integer+, or a type object
# to be used for this attribute. See the examples below for more
# information about providing custom type objects.
#
# ==== Options
# The following options are accepted:
#
# +default+ The default value to use when no value is provided. If this option
# is not passed, the previous default value (if any) will be used.
# Otherwise, the default will be +nil+.
#
# +array+ (PG only) specifies that the type should be an array (see the examples below).
#
# +range+ (PG only) specifies that the type should be a range (see the examples below).
#
# ==== Examples
#
# The type detected by Active Record can be overridden.
#
# # db/schema.rb
# create_table :store_listings, force: true do |t|
# t.decimal :price_in_cents
# end
#
# # app/models/store_listing.rb
# class StoreListing < ActiveRecord::Base
# end
#
# store_listing = StoreListing.new(price_in_cents: '10.1')
#
# # before
# store_listing.price_in_cents # => BigDecimal.new(10.1)
#
# class StoreListing < ActiveRecord::Base
# attribute :price_in_cents, :integer
# end
#
# # after
# store_listing.price_in_cents # => 10
#
# A default can also be provided.
#
# create_table :store_listings, force: true do |t|
# t.string :my_string, default: "original default"
# end
#
# StoreListing.new.my_string # => "original default"
#
# class StoreListing < ActiveRecord::Base
# attribute :my_string, :string, default: "new default"
# end
#
# StoreListing.new.my_string # => "new default"
#
# Attributes do not need to be backed by a database column.
#
# class MyModel < ActiveRecord::Base
# attribute :my_string, :string
# attribute :my_int_array, :integer, array: true
# attribute :my_float_range, :float, range: true
# end
#
# model = MyModel.new(
# my_string: "string",
# my_int_array: ["1", "2", "3"],
# my_float_range: "[1,3.5]",
# )
# model.attributes
# # =>
# {
# my_string: "string",
# my_int_array: [1, 2, 3],
# my_float_range: 1.0..3.5
# }
#
# ==== Creating Custom Types
#
# Users may also define their own custom types, as long as they respond
# to the methods defined on the value type. The method
# +type_cast_from_database+ or +type_cast_from_user+ will be called on
# your type object, with raw input from the database or from your
# controllers. See ActiveRecord::Type::Value for the expected API. It is
# recommended that your type objects inherit from an existing type, or
# from ActiveRecord::Type::Value
#
# class MoneyType < ActiveRecord::Type::Integer
# def type_cast_from_user(value)
# if value.include?('$')
# price_in_dollars = value.gsub(/\$/, '').to_f
# super(price_in_dollars * 100)
# else
# super
# end
# end
# end
#
# class StoreListing < ActiveRecord::Base
# attribute :price_in_cents, MoneyType.new
# end
#
# store_listing = StoreListing.new(price_in_cents: '$10.00')
# store_listing.price_in_cents # => 1000
#
# For more details on creating custom types, see the documentation for
# ActiveRecord::Type::Value.
#
# ==== Querying
#
# When ActiveRecord::QueryMethods#where is called, it will
# use the type defined by the model class to convert the value to SQL,
# calling +type_cast_for_database+ on your type object. For example:
#
# class Money < Struct.new(:amount, :currency)
# end
#
# class MoneyType < Type::Value
# def initialize(currency_converter)
# @currency_converter = currency_converter
# end
#
# # value will be the result of +type_cast_from_database+ or
# # +type_cast_from_user+. Assumed to be in instance of +Money+ in
# # this case.
# def type_cast_for_database(value)
# value_in_bitcoins = @currency_converter.convert_to_bitcoins(value)
# value_in_bitcoins.amount
# end
# end
#
# class Product < ActiveRecord::Base
# currency_converter = ConversionRatesFromTheInternet.new
# attribute :price_in_bitcoins, MoneyType.new(currency_converter)
# end
#
# Product.where(price_in_bitcoins: Money.new(5, "USD"))
# # => SELECT * FROM products WHERE price_in_bitcoins = 0.02230
#
# Product.where(price_in_bitcoins: Money.new(5, "GBP"))
# # => SELECT * FROM products WHERE price_in_bitcoins = 0.03412
#
# ==== Dirty Tracking
#
# The type of an attribute is given the opportunity to change how dirty
# tracking is performed. The methods +changed?+ and +changed_in_place?+
# will be called from ActiveModel::Dirty. See the documentation for those
# methods in ActiveRecord::Type::Value for more details.
def attribute(name, cast_type, **options)
name = name.to_s
reload_schema_from_cache
self.attributes_to_define_after_schema_loads =
attributes_to_define_after_schema_loads.merge(
name => [cast_type, options]
)
end
# This is the low level API which sits beneath +attribute+. It only
# accepts type objects, and will do its work immediately instead of
# waiting for the schema to load. Automatic schema detection and
# ClassMethods#attribute both call this under the hood. While this method
# is provided so it can be used by plugin authors, application code
# should probably use ClassMethods#attribute.
#
# +name+ The name of the attribute being defined. Expected to be a +String+.
#
# +cast_type+ The type object to use for this attribute.
#
# +default+ The default value to use when no value is provided. If this option
# is not passed, the previous default value (if any) will be used.
# Otherwise, the default will be +nil+.
#
# +user_provided_default+ Whether the default value should be cast using
# +type_cast_from_user+ or +type_cast_from_database+.
def define_attribute(
name,
cast_type,
default: NO_DEFAULT_PROVIDED,
user_provided_default: true
)
attribute_types[name] = cast_type
define_default_attribute(name, default, cast_type, from_user: user_provided_default)
end
def load_schema! # :nodoc:
super
attributes_to_define_after_schema_loads.each do |name, (type, options)|
if type.is_a?(Symbol)
type = connection.type_for_attribute_options(type, **options.except(:default))
end
define_attribute(name, type, **options.slice(:default))
end
end
private
NO_DEFAULT_PROVIDED = Object.new # :nodoc:
private_constant :NO_DEFAULT_PROVIDED
def define_default_attribute(name, value, type, from_user:)
if value == NO_DEFAULT_PROVIDED
default_attribute = _default_attributes[name].with_type(type)
elsif from_user
default_attribute = Attribute.from_user(name, value, type)
else
default_attribute = Attribute.from_database(name, value, type)
end
_default_attributes[name] = default_attribute
end
end
end
end
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