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Instance Public methods
serialize(attr_name, class_name_or_coder = Object)

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.


  • 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.


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

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

# Serialize preferences as Hash using YAML coder.
class User < ActiveRecord::Base
  serialize :preferences, Hash
# File activerecord/lib/active_record/attribute_methods/serialization.rb, line 59
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
  elsif [:load, :dump].all? { |x| class_name_or_coder.respond_to?(x) }
    Coders::YAMLColumn.new(attr_name, class_name_or_coder)

  decorate_attribute_type(attr_name, :serialize) do |type|
    if type_incompatible_with_serialize?(type, class_name_or_coder)
      raise ColumnNotSerializableError.new(attr_name, type)

    Type::Serialized.new(type, coder)