Compile error when using CriteriaBuilder

Question

I am trying convert this JPA QL to criteria builder. JBoss 6.0.

"SELECT ba FROM BankAccount ba WHERE ba.balance >= :amt ORDER BY ba.ownerName ASC"

I wrote this code according to several tutorials.

public List<BankAccount> findWithBalance(int amount) {
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<BankAccount> cq = cb.createQuery(BankAccount.class);
    Root<BankAccount> from = cq.from(BankAccount.class);

    ParameterExpression<Integer> balance = cb.parameter(Integer.class);
    cq.select(from);

    Predicate predicate = cb.gt(from.get("balance"), balance);
    cq.where(predicate);

    cq.orderBy(cb.asc(from.get("ownerName")));

    TypedQuery<BankAccount> query = em.createQuery(cq);

    return query.getResultList();
}

But, I am getting a compile error in the line:

Predicate predicate = cb.gt(from.get("balance"), balance);

The error is:

The method gt(Expression<? extends Number>, Expression<? extends Number>) in the type CriteriaBuilder is not applicable for the arguments (Path<Object>, ParameterExpression<Integer>)

RajV · Accepted Answer · 2012-05-03T19:41:32.977

Well, I finally found the right way to call the gt() method. Here is the complete solution. Fully tested in JBoss 6.

public List<BankAccount> findWithBalance(int amount) {
    CriteriaBuilder cb = em.getCriteriaBuilder();
    CriteriaQuery<BankAccount> cq = cb.createQuery(BankAccount.class);
    Root<BankAccount> from = cq.from(BankAccount.class);

    ParameterExpression<Integer> balance = cb.parameter(Integer.class);
    cq.select(from);

    //Here is the trick!
    Predicate predicate = cb.gt(from.<Integer> get("balance"), balance);

    cq.where(predicate);
    cq.orderBy(cb.asc(from.get("ownerName")));

    TypedQuery<BankAccount> query = em.createQuery(cq);

    query.setParameter(balance, amount);

    return query.getResultList();
}

Nayan Wadekar · Answer 2 · 2012-05-03T19:31:59.737

3

The type safety feature in JPA restricts such comparisons with incompatible types, the compiler itself will raise error.

Here, from.get("balance") returns the Path<Object>, but the method can accept parameter of type java.lang.Number, therefore results in error.

You can try the below code.

//--
    Metamodel metamodel = em.getMetamodel();
    EntityType<BankAccount> pClass = metamodel.entity(BankAccount.class);
    Predicate predicate = cb.gt(from.get(pClass.getSingularAttribute("balance", Integer.class)), balance);
//--

If you are using Metamodel API, then you can retieve directly by specifying ClassName_.field as cb.gt(from.get(BankAccount_.balance), balance) which is much cleaner & easy to debug.

But if you are having many entities, then it may be difficult to write their Metamodel classes manually, if the JPA provider doesn't generate them.

edited May 03 '12 at 19:31

answered May 02 '12 at 21:00

Nayan Wadekar

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I made that change. The new error is: The method gt(Expression extends Number>, Expression extends Number>) in the type CriteriaBuilder is not applicable for the arguments (SingularAttribute, ParameterExpression) – RajV May 03 '12 at 18:34
I posted my answer. Please see above. – RajV May 03 '12 at 19:41
@RajV Yes, its much better +1 – Nayan Wadekar May 03 '12 at 20:09

score 0 · Answer 3 · edited Aug 18 '12 at 19:47

0

The compiler is complaining because amount is an int, not an Expression, see if you can figure out how to build an Expression that's a constant and use that and you should be good.

edited Aug 18 '12 at 19:47

Bart

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answered Apr 30 '12 at 21:12

Francis Upton IV

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Can you edit your post with the revised code and give the error message you are currently getting. I can't imagine you are getting the same error if you are using an arg that is a ParameterExpression. And also doing that is probably not what you want. – Francis Upton IV Apr 30 '12 at 23:32
I updated the code and the new error message. What I am doing is straight from various tutorials. I don't think criteria query can be done in JBoss 6. – RajV May 01 '12 at 13:39

Compile error when using CriteriaBuilder

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