CODEWITHSUNDEEP
javahibernatejpa
fancyplants
fancyplants

Reputation: 1727

JPA CriteriaQuery Join - how to join on a subelement?

I am trying to use criteria queries to perform a join.

My class structure is like this:

@Entity
class Parent {
  Intermediate intermediate;
}

@Entity
class Intermediate {
  Set<Child> children
}

@Entity
class Child {
  String someProperty;
}

I am trying to get all parents where at least one child has a matching property, but cannot work out how to do the joining. If the Intermediate object wasn't there, it would be quite easy:

// Here, Intermediate doesn't exist - Parent has the Set<Child> property

CriteriaBuilder builder = ...
CriteriaQuery<Parent> query = ...
Root<Parent> root = query.from( Parent.class );
Join<Parent, Child> join = root.join( "child" );

Path path = join.get( "someProperty" );
Predicate predicate = builder.equal( path, "somevalue" );

But doing this with the intermediate entity breaks it

CriteriaBuilder builder = ...
CriteriaQuery<Parent> query = ...
Root<Parent> root = query.from( Parent.class );
Join<Parent, Child> join = root.join( "intermediate.child" ); <-- Fails

Caused by: java.lang.IllegalArgumentException: Unable to resolve attribute [intermediate.child] against path
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.unknownAttribute(AbstractPathImpl.java:120) ~[hibernate-entitymanager-4.2.0.Final.jar:4.2.0.Final]
    at org.hibernate.ejb.criteria.path.AbstractPathImpl.locateAttribute(AbstractPathImpl.java:229) ~[hibernate-entitymanager-4.2.0.Final.jar:4.2.0.Final]
    at org.hibernate.ejb.criteria.path.AbstractFromImpl.join(AbstractFromImpl.java:411) ~[hiberna

te-entitymanager-4.2.0.Final.jar:4.2.0.Final]

I can work out the Path object for the child in this example, but JPA doesn't seem to want to let me make a Join using a Path object instead of a Root one.

Can anyone help me please? Thanks

Upvotes: 4

Views: 4550

Answers (1)

Koitoer
Koitoer

Reputation: 19543

I think your classes need to be something like this.

@Entity
class Parent {
  @OneToOne
  Intermediate intermediate;
}

@Entity
class Intermediate {
  @OneToOne(mappedBy="intermediate")
  Parent parent;
  @OneToOne
  Set<Child> children
}

@Entity
class Child {
  String someProperty;
}

Then you can do the join as it follows.

CriteriaBuilder builder = ...
CriteriaQuery<Parent> query = ...
Root<Parent> root = query.from( Parent.class );
Join<Parent, Child> join = root.join("intermediate").join("children");

Upvotes: 3

Related Questions