使用CriteriaBuilder时编译错误 [英] Compile error when using CriteriaBuilder

问题描述

我正在尝试将此JPA QL转换为条件构建器。 JBoss 6.0。

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"

我根据几个教程编写了这段代码。

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();
}

但是，我收到了编译错误：

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

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>)

推荐答案

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。

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();
}

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