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serialization.rb
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serialization.rb
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# frozen_string_literal: true
module ActiveRecord
module AttributeMethods
module Serialization
extend ActiveSupport::Concern
class ColumnNotSerializableError < StandardError
def initialize(name, type)
super <<~EOS
Column `#{name}` of type #{type.class} does not support `serialize` feature.
Usually it means that you are trying to use `serialize`
on a column that already implements serialization natively.
EOS
end
end
module ClassMethods
# If you have an attribute that needs to be saved to the database as a
# serialized object, and retrieved by deserializing into the same object,
# then specify the name of that attribute using this method and serialization
# will be handled automatically.
#
# The serialization format may be YAML, JSON, or any custom format using a
# custom coder class.
#
# Keep in mind that database adapters handle certain serialization tasks
# for you. For instance: +json+ and +jsonb+ types in PostgreSQL will be
# converted between JSON object/array syntax and Ruby +Hash+ or +Array+
# objects transparently. There is no need to use #serialize in this
# case.
#
# For more complex cases, such as conversion to or from your application
# domain objects, consider using the ActiveRecord::Attributes API.
#
# ==== Parameters
#
# * +attr_name+ - The name of the attribute to serialize.
# * +class_name_or_coder+ - Optional. May be one of the following:
# * <em>default</em> - The attribute value will be serialized as YAML.
# The attribute value must respond to +to_yaml+.
# * +Array+ - The attribute value will be serialized as YAML, but an
# empty +Array+ will be serialized as +NULL+. The attribute value
# must be an +Array+.
# * +Hash+ - The attribute value will be serialized as YAML, but an
# empty +Hash+ will be serialized as +NULL+. The attribute value
# must be a +Hash+.
# * +JSON+ - The attribute value will be serialized as JSON. The
# attribute value must respond to +to_json+.
# * <em>custom coder</em> - The attribute value will be serialized
# using the coder's <tt>dump(value)</tt> method, and will be
# deserialized using the coder's <tt>load(string)</tt> method. The
# +dump+ method may return +nil+ to serialize the value as +NULL+.
#
# ==== Options
#
# * +: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+.
#
# ==== Examples
#
# ===== Serialize the +preferences+ attribute using YAML
#
# class User < ActiveRecord::Base
# serialize :preferences
# end
#
# ===== Serialize the +preferences+ attribute using JSON
#
# class User < ActiveRecord::Base
# serialize :preferences, JSON
# end
#
# ===== Serialize the +preferences+ +Hash+ using YAML
#
# class User < ActiveRecord::Base
# serialize :preferences, Hash
# end
#
# ===== Serialize the +preferences+ attribute using a custom coder
#
# class Rot13JSON
# def self.rot13(string)
# string.tr("a-zA-Z", "n-za-mN-ZA-M")
# end
#
# # Serializes an attribute value to a string that will be stored in the database.
# def self.dump(value)
# rot13(ActiveSupport::JSON.dump(value))
# end
#
# # Deserializes a string from the database to an attribute value.
# def self.load(string)
# ActiveSupport::JSON.load(rot13(string))
# end
# end
#
# class User < ActiveRecord::Base
# serialize :preferences, Rot13JSON
# end
#
def serialize(attr_name, class_name_or_coder = Object, **options)
# When ::JSON is used, force it to go through the Active Support JSON encoder
# to ensure special objects (e.g. Active Record models) are dumped correctly
# using the #as_json hook.
coder = if class_name_or_coder == ::JSON
Coders::JSON
elsif [:load, :dump].all? { |x| class_name_or_coder.respond_to?(x) }
class_name_or_coder
else
Coders::YAMLColumn.new(attr_name, class_name_or_coder)
end
attribute(attr_name, **options) do |cast_type|
if type_incompatible_with_serialize?(cast_type, class_name_or_coder)
raise ColumnNotSerializableError.new(attr_name, cast_type)
end
cast_type = cast_type.subtype if Type::Serialized === cast_type
Type::Serialized.new(cast_type, coder)
end
end
private
def type_incompatible_with_serialize?(type, class_name)
type.is_a?(ActiveRecord::Type::Json) && class_name == ::JSON ||
type.respond_to?(:type_cast_array, true) && class_name == ::Array
end
end
end
end
end