Revision as of 12:27, 16 June 2010

Fetch Type

By default, EclipseLink persistence provider uses a fetch type of javax.persitence.FetchType.EAGER: this is a requirement on the persistence provider runtime that data must be eagerly fetched.If the default is inappropriate for your application or a particular persistent field, set fetch to FetchType.LAZY: this is a hint to the persistence provider that data should be fetched lazily when it is first accessed (if possible). We recommend using the FetchType.LAZY on all relationships.

You are not required to provide value for this attribute.

How to Configure Default Fetch Group Behavior

You can optionally designate at most one fetch group as the default fetch group for a descriptor's reference class.

If you execute a ReadObjectQuery or ReadAllQuery without specifying a fetch group, EclipseLink will use the default fetch group unless you configure the query otherwise, as this example shows.

Configuring Default Fetch Group Behavior

// at the descriptor level
FetchGroup group = new FetchGroup("nameOnly");
group.addAttribute("firstName");
group.addAttribute("lastName");
employeeDescriptor.getFetchGroupManager().addFetchGroup(group);
// set the default fetch group
employeeDescriptor.getFetchGroupManager().setDefaultFetchGroup(group);

// when query1 is executed, the default fetch group applies
ReadAllQuery query1 = new ReadAllQuery(Employee.class);

// when query2 is executed, the default fetch group does not apply
ReadAllQuery query2 = new ReadAllQuery(Employee.class);
query2.setShouldUsedefaultFetchGroup(false);