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prefetchselect-queryapache-cayenne

Prefetchs with Cayenne

I've got an object of the class A in 2 ways relationships with objects of classes B, C and D.

So I could do (with "a" an object of type A):

B b = a.getB();
A a1 = a.getB().getA(); // and a1 would be equal to a

When I do a SelectQuery on A with prefetchs on the relationship from A to B, C and D, all is fine. But If I add a prefetch on the relationship from B to A, then A lose the relationship from A to C and D or it doesn't do anything. I mean by "lose" that they have been invalidated.

Is that normal? Why is it so?

Notes: I'm using Cayenne 3.0.2 and disjoint prefetchs semantics.

Example 1 (as explained above):

SelectQuery query = new SelectQuery(A.class);
query.addPrefetch("b").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
query.addPrefetch("c").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
query.addPrefetch("d").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
query.addPrefetch("b.a").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
List<?> res= context.performQuery(query);

Example 2 (which is probably the same problem):

SelectQuery query = new SelectQuery(A.class);
query.addPrefetch("b").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
query.addPrefetch("c").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
List<?> res= context.performQuery(query);

then later

SelectQuery query = new SelectQuery(A.class);
query.addPrefetch("d").setSemantics(PrefetchTreeNode.DISJOINT_PREFETCH_SEMANTICS);
List<?> res= context.performQuery(query);

then the relationships with b and c are invalidated or the last prefetch is ignored. Sometimes b and c would be set to null though they are not null.

thanks

Solution

  • After some research, this appears to be the problem discussed in CAY-1695 Jira. It is caused by same objects appearing in the main query and subqueries, confusing prefetch processing code. The fix is only available on master (i.e. 3.2) and is not yet officially released. So one way to get it is to clone Cayenne from GitHub and do your own build. (But ping me if you run into trouble with that, I can post the binaries somewhere).