values_for¶ ↑

values_for is an ActiveRecord extension enabling the easy use of enumerated types for your models.

values_for makes your ActiveRecord-backed class work with an enumerable type. Instead of existing ActiveRecord plugins such as enum_fu, which store the enumerable attribute as an integer, values_for stores the content of the enumerable attribute in a varchar column of the database. The field will automatically validate using validates_inclusion_of and accepts all the same options.

values_for will also optionally create named scopes, predicate methods, and constants defining the possible values for enumerable types on your model. By default, however, it avoids polluting your model with things you may not need unless these features are specifically requested.

values_for is available as a gem available on GitHub. Install with:

sudo gem install mcommons-values_for

You’ll probable want a line like the following in your environment.rb:

config.gem 'mcommons-values_for', :lib => 'values_for'

The following example sets up an enumerable attribute on an ActiveRecord model. This assumes that a previous migration has created a column of type VARCHAR on the table “taco”.

class Taco < ActiveRecord::Base
  values_for :state, :has => [ :new, :composed, :served, :eaten ]
end

For all values_for-enabled models, valid states are able to be read for an attribute by calling the plural of the attribute name:

>> Taco.states
=> [ :new, :composed, :served, :eaten ]

values_for automatically runs validates_inclusion_of on this field. All the validates_inclusion_of options are supported. For example, you can pass :allow_nil=>true to allow the field to be nil.

values_for will optionally create named scopes, predicate methods, and constants defining values for enumerable types on your model. These may be specified on a case-by-case basis by using the :add option. As an example, the following would create an enumerable attribute called “flavor” with the possible values “sour” and “sweet”, while creating named scopes, predicate methods, and constants on your class:

values_for :flavor, :has => [ :sour, :sweet ], :add => [ :named_scopes, :predicate_methods, :constants ]

The different additive options are described below.

The named_scopes option adds a named scope, with either the default or custom prefix, to your model. For example, the following model definition would create a named_scope Taco.flavor_sour on your class:

class Taco < ActiveRecord::Base
  values_for :flavor, :has => [ :sour, :sweet ], :add => :named_scopes
end

Afterwards, you may use the named scopes as follows. Remember to add the prefix!

Taco.flavor_sour
Taco.flavor_sweet

The prefix may be overridden or omitted by using the :prefix option.

values_for also creates predicate methods on instances of your class so that you can ask if they have any of the given enumerable states. For example, if a Taco class has an enumerable type :taste with values :good and :bad, taco.good? would return a boolean value indicating whether or not the taste is good.

This option is only enabled when the additive option predicate_methods is specified.

values_for optionally defines constants corresponding to each of the valid enumerable types on your model. For example, if you have an enumerable column called “states” with valid states :starting and :finished, values_for would define constants on your model Model::STATE_STARTING and Model::STATE_FINISHED with the contents of these constants :starting and :finished respectively. This is only enabled when the additive option :constants is specified.

values_for by default adds the attribute being modified as a prefix to constant declarations, named scopes, and predicate methods. If you wish to modify this prefix, pass the :prefix option to values_for. You may also omit the addition of the prefix by passing :prefix => nil to values_for. Example:

class Taco < ActiveRecord::Base
  values_for :state, :has => [ :new, :composed, :served, :eaten ], :prefix => 'wacky'
end

This makes Taco respond to named scopes like Taco.wacky_composed instead of the default, which would have prefixed the named_scopes with the name of the attribute.

This plugin doesn’t implement default values for a model. If this behavior is desired, you may be interested in the default_value_for plugin (available github.com/FooBarWidget/default_value_for/tree/master), which has been successfully tested with values_for.

Mal McKay, Justin Leitgeb and Ben Stein