EclipseLink/Examples/JPA/QueryOptimization

EclipseLink gives users the option to optimize their queries using batch and joined reading through the use of a query hints.

See:

• Optimizing Queries in the EclipseLink User's Guide
• Using EclipseLink JPA Query Customization Extensions in the EclipseLink User's Guide
• How to Use Batch and Join Reading in the EclipseLink User's Guide
• org.eclipse.persistence.config.QueryHints
• Batch fetch example - download link - SVN

• Blog: Batch fetching - optimizing object graph loading

Batch Reading (Fetching)

Configures the query to optimize the retrieval of the related objects, the related objects for all the resulting objects will be read in a single query (instead of n queries). Valid values are strings that represent JPQL style navigations to a relationship. e.g. e.manager.phoneNumbers

Via Annotations

@Entity
@Table(name="JPA_EMPLOYEE")
@NamedQuery(
  name="findAllEmployees",
  query="SELECT e FROM Employee e order by e.id"),
  hints={
    @QueryHint(
      name=QueryHints.BATCH, 
      value="e.manager.phoneNumbers")
  }
)
public class Employee implements Serializable {
...
 
}

Via XML

<entity name="Employee" class="org.eclipse.testing.Employee" access="PROPERTY">
  ...
  <named-query name="findAllEmployees">
    <query>SELECT e FROM Employee e order by e.id</query>
    <hint name="eclipselink.batch" value="e.manager.phoneNumbers">
  </named-query>
  ...
</entity>

Joined Reading (Fetching)

Configures the query to optimize the retrieval of the related objects, the related objects will be joined into the query instead of being queried independently. This allows for nested join fetching which is not supported in JPQL. Valid values are strings that represent JPQL style navigations to a relationship. e.g. e.manager.phoneNumbers

Via Annotations

@Entity
@Table(name="JPA_EMPLOYEE")
@NamedQuery(
  name="findAllEmployeesByFirstName",
  query="SELECT OBJECT(employee) FROM Employee employee WHERE employee.firstName = :firstname"),
  hints={
    @QueryHint(
      name=QueryHints.FETCH, 
      value="e.manager.phoneNumbers")
  }
)
public class Employee implements Serializable {
...
 
}

Via XML

<entity name="Employee" class="org.eclipse.testing.Employee" access="PROPERTY">
  ...
  <named-query name="findAllEmployeesByFirstName">
    <query>SELECT OBJECT(employee) FROM Employee employee WHERE employee.firstName = :firstname</query>
    <hint name="eclipselink.join-fetch" value="e.manager.phoneNumbers">
  </named-query>
  ...
</entity>