# module ActiveRecord::AttributeMethods::Serialization::ClassMethods

### Public Instance Methods

serialize(attr_name, class_name_or_coder = Object) click to toggle source

If you have an attribute that needs to be saved to the database as an object, and retrieved as the same object, then specify the name of that attribute using this method and it will be handled automatically. The serialization is done through YAML. If `class_name` is specified, the serialized object must be of that class on assignment and retrieval. Otherwise SerializationTypeMismatch will be raised.

Empty objects as `{}`, in the case of `Hash`, or `[]`, in the case of `Array`, will always be persisted as null.

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 field name that should be serialized.

- `class_name_or_coder` - Optional, a coder object, which responds to `.load` and `.dump` or a class name that the object type should be equal to.

#### Example¶ ↑

    # Serialize a preferences attribute.
    class User < ActiveRecord::Base
      serialize :preferences
    end

    # Serialize preferences using JSON as coder.
    class User < ActiveRecord::Base
      serialize :preferences, JSON
    end

    # Serialize preferences as Hash using YAML coder.
    class User < ActiveRecord::Base
      serialize :preferences, Hash
    end

    # File lib/active_record/attribute_methods/serialization.rb, line 48
    def serialize(attr_name, class_name_or_coder = Object)
      # 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

      decorate_attribute_type(attr_name, :serialize) do |type|
        Type::Serialized.new(type, coder)
      end
    end