A workaround of Google App Engine's limitations regarding Criteria joins

gae-joins.java

CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery<Foo> q = cb.createQuery(Foo.class);
Root<Foo> foo = q.from(Foo.class);

foo.join("bar").alias("b1");
foo.alias("b1");
q.select(foo).where(cb.equal(foo.get("id"), "42"));
foo.alias("f1");

TypedQuery<Foo> query = em.createQuery(q);
List<Foo> foos = query.getResultList();

The resulting statement is equivalent to:

SELECT f FROM Foo f JOIN f.bar b WHERE b.id = "42"