Module: ActiveRecord::Attributes::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 toActiveRecord::Base.where. This will let you use your domain objects across much of Active Record, without having to rely on implementation details or monkey patching.

Parameters

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. If this parameter is not passed, the previously defined type (if any) will be used. Otherwise, the type will be ::ActiveModel::Type::Value. See the examples below for more information about providing custom type objects.

Options

:default : The default value to use when no value is provided. If this option is not passed, the previously defined default value (if any) on the superclass or in the schema will be used. Otherwise, the default will be nil.

:array : (PostgreSQL only) Specifies that the type should be an array. See the examples below.

:range : (PostgreSQL only) Specifies that the type should be a range. See the examples below.

When using a symbol for cast_type, extra options are forwarded to the constructor of the type object.

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(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.

#### db/schema.rb
create_table :store_listings, force: true do |t|
  t.string :my_string, default: "original default"
end

{StoreListing.new}.my_string # => "original default"

#### app/models/store_listing.rb
class StoreListing < {ActiveRecord::Base}
  attribute :my_string, :string, default: "new default"
end

{StoreListing.new}.my_string # => "new default"

class Product < {ActiveRecord::Base}
  attribute :my_default_proc, :datetime, default: -> { Time.now }
end

{Product.new}.my_default_proc # => 2015-05-30 11:04:48 -0600
sleep 1
{Product.new}.my_default_proc # => 2015-05-30 11:04:49 -0600

Attributes do not need to be backed by a database column.

#### app/models/my_model.rb
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
  }

Passing options to the type constructor

#### app/models/my_model.rb
class MyModel < {ActiveRecord::Base}
  attribute :small_int, :integer, limit: 2
end

{MyModel.create}(small_int: 65537)
#### => Error: 65537 is out of range for the limit of two bytes

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 deserialize or cast will be called on your type object, with raw input from the database or from your controllers. See ::ActiveModel::Type::Value for the expected API. It is recommended that your type objects inherit from an existing type, or from Type::Value

class PriceType < {ActiveRecord::Type::Integer}
  def cast(value)
    if !value.kind_of?(Numeric) && value.include?('$')
      price_in_dollars = value.gsub(/\$/, '').to_f
      super(price_in_dollars * 100)
    else
      super
    end
  end
end

#### config/initializers/types.rb
{ActiveRecord::Type.register}(:price, PriceType)

#### app/models/store_listing.rb
class StoreListing < {ActiveRecord::Base}
  attribute :price_in_cents, :price
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 ::ActiveModel::Type::Value. For more details on registering your types to be referenced by a symbol, see Type.register. You can also pass a type object directly, in place of a symbol.

Querying

WhenActiveRecord::Base.where is called, it will use the type defined by the model class to convert the value to SQL, calling serialize on your type object. For example:

class Money < {Struct.new}(:amount, :currency)
end

class PriceType < {ActiveRecord::Type::Value}
  def initialize(currency_converter:)
    @currency_converter = currency_converter
  end

  # value will be the result of #deserialize or
  # #cast. Assumed to be an instance of Money in
  # this case.
  def serialize(value)
    value_in_bitcoins = @currency_converter.convert_to_bitcoins(value)
    value_in_bitcoins.amount
  end
end

#### config/initializers/types.rb
{ActiveRecord::Type.register}(:price, PriceType)

#### app/models/product.rb
class Product < {ActiveRecord::Base}
  currency_converter = ConversionRatesFromTheInternet.new
  attribute :price_in_bitcoins, :price, currency_converter: 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 ::ActiveModel::Type::Value for more details.

This API only accepts type objects. While this method is provided so it can be used by plugin authors, application code should probably use #attribute.

Parameters

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. A proc can also be passed, and will be called once each time a new value is needed.

user_provided_default : Whether the default value should be cast using cast or deserialize.

See ActiveModel::Attributes::ClassMethods#type_for_attribute.

This method will access the database and load the model's schema if necessary.