EclipseLink/Examples/JPA/Extensibility

The follow steps will help you configure your persistence unit so that it can have a set of mappings that are changeable after your application is deployed.

1. Design a standard JPA Application

2. Decide which Entities will allow flexible mappings, annotate them as such and provide facilities to store the addional data.

  @Entity
  @VirtualAccessMethods
  public class Customer{
 
...
 
    @Transient
    private Map<String, Object> extensions;
 
    public <T> T get(String name) {
        return (T) extentions.get(name);
    }
 
    public Object set(String name, Object value) {
        return extensions.put(name, value);
    }

3. When you design your schema, provide enough extra columns in your tables to accomodate the number of flexible mappings you will allow. e.g. The following table has 3 predefined columns and 3 columns designed to accomodate mappings added after design (FLEX_COL1, FLEX_COL2, FLEX_COL3)

• CUSTOMER
  • INTEGER ID
  • VARCHAR NAME
  • VARCHAR FLEX_COL1
  • VARCHAR FLEX_COL2
  • VARCHAR FLEX_CO31

4. Deploy your application

5. To provide additional mappings, provide an eclipselink-orm.xml file that contains the additional mappings.

 
   <basic name="idNumber" attribute-type="String">
      <column name="FLEX_1"/>
      <access-methods get-method="get" set-method="set"/>
    </basic>

6. Use persistence unit properties to get your application to use the file:

  <property name="eclipselink.metadata-source" value="XML"/>
  <property name="eclipselink.metadata-source.xml.url" value="foo://bar"/>