Hibernate proxy

Hibernate proxy

Proxies are created dynamically by subclassing your object at runtime. The subclass has all the methods of the parent, and when any of the methods are accessed, the proxy loads up the real object from the DB and calls the method for you. Very nice in simple cases with no object hierarchy. Typecasting and instanceof work perfectly on the proxy in this case since it is a direct subclass. By default Hibernate creates a proxy for each of the class you map in mapping file. This class contain the code to invoke JDBC. This class is created by hibernate using CGLIB.

Proxies are the mechanism that allows Hibernate to break up the interconnected cloud of objects in the database into smaller chunks, that can easily fit in memory. Proxies are created dynamically by subclassing your object at runtime. The subclass has all the methods of the parent, and when any of the methods are accessed, the proxy loads up the real object from the DB and calls the method for you.

A class can be mapped to a proxy instead to a table. When you actually call load on session it returns you proxy. This proxy may contain actual method to load the data. Object proxies can be defined in one of two ways. First, you can add a proxy attribute to the class element. You can either specify a different class or use the persistent class as the proxy.

For example:

<class name="Loc"
proxy="com.ch01.Loc">
lt;/class>

The second method is to use the lazy attribute. Setting lazy="true"is a shorthand way of defining the persistent class as the proxy.