Module: ActiveRecord::NamedScope::ClassMethods

### Home Classes Methods

### In Files

- lib/active_record/named_scope.rb

### Methods

- #named_scope
- #scope
- #scoped
- #scopes
- #valid_scope_name?

### Files

- README.rdoc

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# ActiveRecord::NamedScope::ClassMethods

### Public Instance Methods

named_scope(*args, &block) click to toggle source

    # File lib/active_record/named_scope.rb, line 123
    def named_scope(*args, &block)
      ActiveSupport::Deprecation.warn("Base.named_scope has been deprecated, please use Base.scope instead", caller)
      scope(*args, &block)
    end

scope(name, scope_options = {}, &block) click to toggle source

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')`.

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 be procedural:

    class Shirt < ActiveRecord::Base
      scope :colored, lambda {|color| where(:color => color) }
    end

In this example, `Shirt.colored('puce')` finds all puce 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

    # File lib/active_record/named_scope.rb, line 100
    def scope(name, scope_options = {}, &block)
      name = name.to_sym
      valid_scope_name?(name)

      extension = Module.new(&block) if block_given?

      scopes[name] = lambda do |*args|
        options = scope_options.is_a?(Proc) ? scope_options.call(*args) : scope_options

        relation = if options.is_a?(Hash)
          scoped.apply_finder_options(options)
        elsif options
          scoped.merge(options)
        else
          scoped
        end

        extension ? relation.extending(extension) : relation
      end

      singleton_class.send(:redefine_method, name, &scopes[name])
    end

scoped(options = nil) click to toggle source

Returns an anonymous scope.

    posts = Post.scoped
    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.scoped
    fruits = fruits.where(:colour => 'red') if options[:red_only]
    fruits = fruits.limit(10) if limited?

Anonymous scopes tend to be useful when procedurally generating complex queries, where passing intermediate values (scopes) around as first-class objects is convenient.

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

    # File lib/active_record/named_scope.rb, line 28
    def scoped(options = nil)
      if options
        scoped.apply_finder_options(options)
      else
        current_scoped_methods ? relation.merge(current_scoped_methods) : relation.clone
      end
    end

scopes() click to toggle source

    # File lib/active_record/named_scope.rb, line 36
    def scopes
      read_inheritable_attribute(:scopes) || write_inheritable_attribute(:scopes, {})
    end

### Protected Instance Methods

valid_scope_name?(name) click to toggle source

    # File lib/active_record/named_scope.rb, line 130
    def valid_scope_name?(name)
      if !scopes[name] && respond_to?(name, true)
        logger.warn "Creating scope :#{name}. "                        "Overwriting existing method #{self.name}.#{name}."
      end
    end

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