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Lazy loaded references

Daniel Merwin edited this page Aug 28, 2016 · 3 revisions

Morphium's Lazy Loading of references

morphium supports lazy loading of references. This is easy to use, just add @Reference(lazyLoading=true) to the reference you want to have lazy loaded.

@Entity
public class MyEntity {
   ....
   @Reference(lazyLoading=true)
   private UncachedObject myReference;  //will be loaded when first accessed
   @Reference
   private MyEntity ent; //will be loaded when this object is loaded - use with caution
                         //this could cause an endless loop
   private MyEntity embedded; //this object is not available on its own
                              //its embedded as subobject in this one
}

how does it work

When a reference is being lazy loaded, the corresponding field will be set with a Proxy for an instance of the correct type, where only the ObjectID is set. Any access to it will be catched by the proxy, and any method will cause the object to be read from DB and unmarshalled. Hence this object will only be loaded upon first access.

It should be noted that when using Object.toString(); for testing that the object will be loaded from the database and appear to not be lazy loaded. In order to test Lazy Loading you should load the base object with the lazy reference and access it directly and it will be null. Additionally the referenced object will be null until the references objects fields are accessed.

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