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Annotation Inheritance in Morphium

Stephan Bösebeck edited this page Aug 23, 2013 · 2 revisions

Annotation Inheritence

By default, Java does not support the inheritence of Annotations. This is ok in most cases, but in the case of entities it's a bugger. I added inheritence to morphium to be able to build flexible data structures and store them to mongo.

Implementation

Well, it's quite easy, actually ;-) The algorithm for getting the inherited annotations looks as follows (simplified)

Take the annotations from the current class, if found, return it Take the superclass, if superclass is "Object" return null if there is the annotation to look for, return it continue with step 1 This way, all annotations in the hierarchy are taken into account and the most recent one is taken. You can always change the annotations when subclassing, although you cannot "erase" them (which means, if you inherit from an entity, it's always an entity). For Example:

   @Entity 
   @NoCache
   public class Person {
      @Id
      private ObjectId id;
     ....
   }

And the subclass:

   @Cache(writeCache=true, readCache=false)
   public class Parent {
      @Reference
      private List<Person> parentFrom;
      ...
   }

Please keep in mind, that unless specified otherwise, the classname will be taken as the name for your collection. Also, be sure to store your classname in the collection (set polymorph=true in @Entity annotation) if you want to store them in one collection.

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