Module: WillPaginate::NamedScope::ClassMethods
- Defined in:
- lib/will_paginate/finders/active_record/named_scope.rb
Instance Method Summary collapse
-
#named_scope(name, options = {}, &block) ⇒ Object
Adds a class method for retrieving and querying objects.
- #scopes ⇒ Object
Instance Method Details
#named_scope(name, options = {}, &block) ⇒ Object
Adds a class method for retrieving and querying objects. A scope represents a narrowing of a database query, such as :conditions => {:color => :red}, :select => 'shirts.*', :include => :washing_instructions
.
class Shirt < ActiveRecord::Base
named_scope :red, :conditions => {:color => 'red'}
named_scope :dry_clean_only, :joins => :washing_instructions, :conditions => ['washing_instructions.dry_clean_only = ?', true]
end
The above calls to named_scope
define class methods Shirt.red
and Shirt.dry_clean_only
. Shirt.red
, in effect, represents the query Shirt.find(:all, :conditions => {: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.find(:first)
, Shirt.red.count
, Shirt.red.find(:all, :conditions => {:size => 'small'})
. Also, just as with the association objects, name scopes acts 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 were 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 descendent 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
named_scope :colored, lambda { |color|
{ :conditions => { :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
named_scope :red, :conditions => {:color => 'red'} do
def dom_id
'red_shirts'
end
end
end
For testing complex named scopes, you can examine the scoping options using the proxy_options
method on the proxy itself.
class Shirt < ActiveRecord::Base
named_scope :colored, lambda { |color|
{ :conditions => { :color => color } }
}
end
= { :conditions => { :colored => 'red' } }
assert_equal , Shirt.colored('red').
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# File 'lib/will_paginate/finders/active_record/named_scope.rb', line 86 def named_scope(name, = {}, &block) name = name.to_sym scopes[name] = lambda do |parent_scope, *args| Scope.new(parent_scope, case when Hash when Proc .call(*args) end, &block) end (class << self; self end).instance_eval do define_method name do |*args| scopes[name].call(self, *args) end end end |
#scopes ⇒ Object
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# File 'lib/will_paginate/finders/active_record/named_scope.rb', line 19 def scopes read_inheritable_attribute(:scopes) || write_inheritable_attribute(:scopes, {}) end |