JPA - 带有“WHERE”子句的CriteriaQuery

Question

I know this can be a very simple question to some of u, but I'm having a hard time trying to find out how to build a simple Select * From X Where Xa = :myparam using a CriteriaBuilder .

Now, this is the code I have managed to build so far:

    CriteriaBuilder cb = getEntityManager().getCriteriaBuilder();
    CriteriaQuery cq = cb.createQuery();

    Root<MyClass1> r = cq.from(MyClass1.class);
    cq.select(r);

    ParameterExpression<Long> p = cb.parameter(Long.class);

    cq.where(cb.equal(r.get("anotherClass.id"), p));

    javax.persistence.Query q = getEntityManager().createQuery(cq);

The class where I am applying this query is this one:

@Entity
public class MyClass1 implements Serializable {
    @Id
    private Long id;
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ANOTHERCLASS_ID")    
    private AnotherClass anotherClass;
    ...
}

@Entity
public class AnotherClass implements Serializable {
    @Id
    private Long id;
    ...
}

I just need to select all records from myclass1 "WHERE" anotherClass.id = 1L , and where do I set the "1L", I know it goes in p but where?

That's all. Looks simple, but I am really not familiar with this CriteriaBuilder thing, so hope you can have some answers.

Thanks.

Answer 1

Parameters are set in Criteria queries the same as in JPQL or native queries, you set them on the Query.

ie

javax.persistence.Query q = getEntityManager().createQuery(cq);
q.setParameter(1, 1L);

Note that you are using a positional parameter, to use a named one pass the name to parameter().

ParameterExpression<Long> p = cb.parameter(Long.class, "id");
...
q.setParameter("id", 1L);

See, http://en.wikibooks.org/wiki/Java_Persistence/Querying#Parameters

Answer 2

you are trying to use a joined table in a where clause expression, so you need to use a join between tghe tables first.

...
Join<MyClass1,ANotherClass> pathA = r.join(MyClass.anotherClass);

...

cb.where(cb.equal(pathA.get(AnotherClass_.id), p));

Provided you have Metamodel classes built. See also Chapter 40 of the Java EE Tutorial.

Regards, Thomas