java - 使用 CriteriaBuilder 时编译错误

Question

我正在尝试将此 JPA QL 转换为条件生成器。 JBoss 6.0。

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

我根据几个教程编写了这段代码。

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();
}

但是，我在行中遇到编译错误:

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

错误是:

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

Answer 1

好吧，我终于找到了调用 gt() 方法的正确方法。这是完整的解决方案。在 JBoss 6 中经过全面测试。

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();
}