diff options
Diffstat (limited to 'railties/guides')
| -rw-r--r-- | railties/guides/source/active_record_querying.textile | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/railties/guides/source/active_record_querying.textile b/railties/guides/source/active_record_querying.textile index 3b4f2befda..21bbc64255 100644 --- a/railties/guides/source/active_record_querying.textile +++ b/railties/guides/source/active_record_querying.textile @@ -608,6 +608,30 @@ SELECT * FROM clients WHERE orders_count > 10 ORDER BY clients.id DESC This method accepts *no* arguments. +h3. Null Relation + +The +none+ method returns a chainable relation with no records. Any subsequent conditions chained to the returned relation will continue generating empty relations. This is useful in scenarios where you need a chainable response to a method or a scope that could return zero results. + +<ruby> +Post.none # returns an empty Relation and fires no queries. +</ruby> + +<ruby> +# The visible_posts method below is expected to return a Relation. +@posts = current_user.visible_posts.where(:name => params[:name]) + +def visible_posts + case role + when 'Country Manager' + Post.where(:country => country) + when 'Reviewer' + Post.published + when 'Bad User' + Post.none # => returning [] or nil breaks the caller code in this case + end +end +</ruby> + h3. Readonly Objects Active Record provides +readonly+ method on a relation to explicitly disallow modification of any of the returned objects. Any attempt to alter a readonly record will not succeed, raising an +ActiveRecord::ReadOnlyRecord+ exception. |