Composite entity pattern

Composite entity is a Java EE Software design pattern and it is used to model, represent, and manage a set of interrelated persistent objects rather than representing them as individual fine-grained entity beans, and also a composite entity bean represents a graph of objects.

Structure

There are a number of strategies to implement composite entity pattern. This pattern mainly composites of composite entity, coarse-grained object, and dependent objects.

Composite entity component

Composite entity is the coarse-grained entity bean which may be the coarse-grained object, or may contain a reference to the coarse-grained object.

Coarse-grained object

A coarse-grained object is an object with its own life cycle manages its own relationships to other objects. It can be an object contained in the composite entity, or, composite entity itself can be the coarse-grained object which holds dependent objects.

Dependent objects

It is an object, which can contain other dependent objects (there may be a tree of objects within the composite entity), that depends on the coarse-grained object and has its life cycle managed by the coarse-grained object.

Consequences

According to Oracle description of the pattern, consequences include eliminating inter-entity relationships, improving manageability by reducing entity beans, improving network performance, reducing database schema dependency, increasing object granularity, facilitating composite transfer object creation and overhead of multi-level dependent object graphs.

Drawbacks

The fatal drawback is the requirement of bean-managed persistent (BMP) bean. This involves more work for developers, and create some problems as follows:
* materializing all the data in a coarse-grained entity whenever it is accessed, is unacceptably expensive
* In Java, implementation of the ejbStore() method needs to be smart enough to avoid issuing all the updates required to persist the entire state of the object, unless the data has changed in all the persistent objects.
Composite entity pattern can only be implemented using BMP or by adding more hand-coded persistence logic to container managed persistence (CMP) beans. These both approaches reduce the maintainability.

Sample code

Sample code for a Professional Service Automation application (PSA) in which the resource object is implemented via composite entity pattern, may look like as follows (entity implements coarse-grained object):

package corepatterns.apps.psa.ejb;

import corepatterns.apps.psa.core.*;
import corepatterns.apps.psa.dao.*;
import java.sql.*;
import javax.sql.*;
import java.util.*;
import javax.ejb.*;
import javax.naming.*;

public class ResourceEntity implements EntityBean

See also

* Data transfer object

References

{{Design Patterns patterns

Software design patterns
Articles with example Java code