Module: ActiveRecord::Scoping::Named::ClassMethods

Defined in:
lib/active_record/scoping/named.rb

Instance Method Summary collapse

Instance Method Details

#all ⇒ Object

Returns an ActiveRecord::Relation scope object.

posts = Post.all
posts.size # Fires "select count(*) from  posts" and returns the count
posts.each {|p| puts p.name } # Fires "select * from posts" and loads post objects

fruits = Fruit.all
fruits = fruits.where(color: 'red') if options[:red_only]
fruits = fruits.limit(10) if limited?

You can define a scope that applies to all finders using ActiveRecord::Base.default_scope.



24
25
26
27
28
29
30
31
32
 
# File 'lib/active_record/scoping/named.rb', line 24

def all
  if current_scope
    current_scope.clone
  else
    scope = relation
    scope.default_scoped = true
    scope
  end
end

#scope(name, body, &block) ⇒ Object

Adds a class method for retrieving and querying objects. A scope represents a narrowing of a database query, such as where(color: :red).select('shirts.*').includes(:washing_instructions).

class Shirt < ActiveRecord::Base
  scope :red, -> { where(color: 'red') }
  scope :dry_clean_only, -> { joins(:washing_instructions).where('washing_instructions.dry_clean_only = ?', true) }
end

The above calls to scope define class methods Shirt.red and Shirt.dry_clean_only. Shirt.red, in effect, represents the query Shirt.where(color: 'red').

You should always pass a callable object to the scopes defined with scope. This ensures that the scope is re-evaluated each time it is called.

Note that this is simply ‘syntactic sugar’ for defining an actual class method:

class Shirt < ActiveRecord::Base
  def self.red
    where(color: 'red')
  end
end

Unlike Shirt.find(...), however, the object returned by Shirt.red is not an Array; it resembles the association object constructed by a has_many declaration. For instance, you can invoke Shirt.red.first, Shirt.red.count, Shirt.red.where(size: 'small'). Also, just as with the association objects, named scopes act like an Array, implementing Enumerable; Shirt.red.each(&block), Shirt.red.first, and Shirt.red.inject(memo, &block) all behave as if Shirt.red really was an Array.

These named scopes are composable. For instance, Shirt.red.dry_clean_only will produce all shirts that are both red and dry clean only. Nested finds and calculations also work with these compositions: Shirt.red.dry_clean_only.count returns the number of garments for which these criteria obtain. Similarly with Shirt.red.dry_clean_only.average(:thread_count).

All scopes are available as class methods on the ActiveRecord::Base descendant upon which the scopes were defined. But they are also available to has_many associations. If,

class Person < ActiveRecord::Base
  has_many :shirts
end

then elton.shirts.red.dry_clean_only will return all of Elton’s red, dry clean only shirts.

Named scopes can also have extensions, just as with has_many declarations:

class Shirt < ActiveRecord::Base
  scope :red, -> { where(color: 'red') } do
    def dom_id
      'red_shirts'
    end
  end
end

Scopes can also be used while creating/building a record.

class Article < ActiveRecord::Base
  scope :published, -> { where(published: true) }
end

Article.published.new.published    # => true
Article.published.create.published # => true

Class methods on your model are automatically available on scopes. Assuming the following setup:

class Article < ActiveRecord::Base
  scope :published, -> { where(published: true) }
  scope :featured, -> { where(featured: true) }

  def self.latest_article
    order('published_at desc').first
  end

  def self.titles
    pluck(:title)
  end
end

We are able to call the methods like this:

Article.published.featured.latest_article
Article.featured.titles



145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
 
# File 'lib/active_record/scoping/named.rb', line 145

def scope(name, body, &block)
  extension = Module.new(&block) if block

  # Check body.is_a?(Relation) to prevent the relation actually being
  # loaded by respond_to?
  if body.is_a?(Relation) || !body.respond_to?(:call)
    ActiveSupport::Deprecation.warn(
      "Using #scope without passing a callable object is deprecated. For " \
      "example `scope :red, where(color: 'red')` should be changed to " \
      "`scope :red, -> { where(color: 'red') }`. There are numerous gotchas " \
      "in the former usage and it makes the implementation more complicated " \
      "and buggy. (If you prefer, you can just define a class method named " \
      "`self.red`.)"
    )
  end

  singleton_class.send(:define_method, name) do |*args|
    if body.respond_to?(:call)
      scope = all.scoping { body.call(*args) }
      scope = scope.extending(extension) if extension
    else
      scope = body
    end

    scope || all
  end
end

#scope_attributes ⇒ Object

Collects attributes from scopes that should be applied when creating an AR instance for the particular class this is called on.



36
37
38
39
40
41
42
43
44
 
# File 'lib/active_record/scoping/named.rb', line 36

def scope_attributes # :nodoc:
  if current_scope
    current_scope.scope_for_create
  else
    scope = relation
    scope.default_scoped = true
    scope.scope_for_create
  end
end

#scope_attributes? ⇒ Boolean

Are there default attributes associated with this scope?

Returns:

  • (Boolean) 


47
48
49
 
# File 'lib/active_record/scoping/named.rb', line 47

def scope_attributes? # :nodoc:
  current_scope || default_scopes.any?
end