Fetch all collections eagerly in JPA

Question

Is it possible to fetch all collections in an entity hierarchy eagerly in a particular query only?

For example,

entity Department has a list of entity Employee. Employee has a list of entity Address and a list of entity Credentials. Department has another list of entity Project.

I want to eagerly fetch all these collections (in my real case there are more collections) in a particular query SELECT dept FROM Department dept and not in other cases (so can't be annotated with FetchType.EAGER). Is it possible?

I am using Eclipselink.

Thanks in advance.

Solution 1

You can use join fetching, batch fetching, or load groups.

I would recommend batch fetching over join fetching, as it will perform significantly better with multiple collections.

See,

http://java-persistence-performance.blogspot.com/2010/08/batch-fetching-optimizing-object-graph.html

Also, http://www.eclipse.org/eclipselink/documentation/2.4/jpa/extensions/q_batch.htm#batch

http://www.eclipse.org/eclipselink/documentation/2.4/jpa/extensions/q_join_fetch.htm#fetch

http://wiki.eclipse.org/EclipseLink/Examples/JPA/AttributeGroup#Load_Examples

Solution 2

Nested fetch joins are not allowed by JPA, you should use the EclipseLink query hint eclipselink.join-fetch. See the answer to this question.

Solution 3

If I recall correctly, you need to use FETCH JOIN statements in your query.

See also: Fetch Joins