diff options
Diffstat (limited to 'activerecord/lib/active_record/relation/query_methods.rb')
-rw-r--r-- | activerecord/lib/active_record/relation/query_methods.rb | 33 |
1 files changed, 33 insertions, 0 deletions
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb index a8ae7208fc..b6d762c2e2 100644 --- a/activerecord/lib/active_record/relation/query_methods.rb +++ b/activerecord/lib/active_record/relation/query_methods.rb @@ -196,6 +196,39 @@ module ActiveRecord relation end + # Returns a chainable relation with zero records, specifically an + # instance of the NullRelation class. + # + # The returned NullRelation inherits from Relation and implements the + # Null Object pattern so it is an object with defined null behavior: + # it always returns an empty array of records and does not query the database. + # + # Any subsequent condition chained to the returned relation will continue + # generating an empty relation and will not fire any query to the database. + # + # This is useful in scenarios where you need a chainable response to a method + # or a scope that could return zero results. + # + # For example: + # + # @posts = current_user.visible_posts.where(:name => params[:name]) + # # => the visible_posts method is expected to return a chainable Relation + # + # def visible_posts + # case role + # when 'Country Manager' + # Post.where(:country => country) + # when 'Reviewer' + # Post.published + # when 'Bad User' + # Post.none # => returning [] instead breaks the previous code + # end + # end + # + def none + NullRelation.new(@klass, @table) + end + def readonly(value = true) relation = clone relation.readonly_value = value |