Serialized Attributes

Typecast

Typecast from Ohm-contrib is deprecated in favor of Serialized which is now part of the core.

Serialized

Serialized is the new module name for typed attributes. It should be mostly source compatible with Typecast, but unlike that approach, it avoids the use of proxies for the values.

With Serialized, model attribute declarations accept a type (class) name:

require 'ohm/serialized'
class User < Ohm::Model
  include Ohm::Serialized
  attribute :name   # String
  attribute :score, Integer
  attribute :last_login, Time
  attribute :opts, Hash
end

Attribute values are serialized from the declared type to String on assignment, and converted back when the attribute is read. The serialization happens using a Serializer based on the declared attribute type.

Often it's nice to have a default value for an attribute rather than nil, such as an empty hash {} for a Hash attribute. This can be accomplished with the default: value option on the attribute declaration, which is then passed through to the serializer.

attribute :opts, Hash, default: {}

You can also pass a Proc, e.g.:

attribute :time, Time, default: -> { Time.now }

The default proc will be passed the current object and the attribute name if its arity allows, i.e.:

attribute :meta, Hash, default: {|obj,att| obj[att] = { this: att } }

Serializers

The new Serialized module uses Serializers to convert primitive values to Strings for writing to the database, and back to objects when read. Serializers are defined for all the basic attribute types, including Integer, Float, Decimal, Boolean, Symbol, Date, Time, Hash, and Array.

The HashSerializer and ArraySerializer use JSON to represent their values as String. This has inherent limitations as sub-objects of these structures are not presently deserialized to objects, but only primitive values. It's easy to define another serialization mechanism, however. See the source for examples.

HashSerializer by default symbolizes its keys on deserialization. To change this for an attribute, use the symbolize_keys: false option when declaring the attribute:

attribute :names, Hash, symbolize_keys: false

The default serializers can be overriden or a custom serializer provided for an attribute with the serializer: option when declaring the attribute:

attribute :start, Time, serializer: MyCustomTimeSerializer

If you define a custom serializer for your own class or to override a default serializer, when you name your serializer either <Class>::Serializer or <Class>Serializer then you won't need to specify it with the serializer: option.

Timestamps

Timestamps is adapted to the core from Ohm-contrib and now persists Time values preserving microseconds:

require 'ohm/timestamps'
class Order < Ohm::Model
  include Ohm::Timestamps
  # defines:
  #   attribute :created_at, Timestamp
  #   attribute :updated_at, Timestamp
end

>> Order.create
=> #<Order:1 created_at="2011-05-26 09:10:40.921490 UTC" updated_at="2011-05-26 09:10:40.921490 UTC">