Module: Sequel::Plugins::IdentityMap
- Defined in:
- lib/sequel/plugins/identity_map.rb
Overview
The identity_map plugin allows the user to create temporary identity maps via the with_identity_map method, which takes a block. Inside the block, objects have a 1-1 correspondence with rows in the database.
For example, the following is true, and wouldn’t be true if you weren’t using the identity map:
Sequel::Model.with_identity_map do
Album.filter{(id > 0) & (id < 2)}.first.object_id == Album.first(:id=>1).object_id
end
In additional to providing a 1-1 correspondence, the identity_map plugin also provides a cached looked up of records in two cases:
-
Model.[] (e.g. Album)
-
Model.many_to_one accessor methods (e.g. album.artist)
If the object you are looking up using one of those two methods is already in the identity map, the record is returned without a database query being issued.
Identity maps are thread-local and only presist for the duration of the block, so they should be should only be considered as a possible performance enhancer.
Defined Under Namespace
Modules: ClassMethods, InstanceMethods