JPA Criteria Builder中的If/Case语句 [英] If/Case statement in JPA Criteria Builder

问题描述

我想建立一个查询，该查询在不同实体上搜索日期.我的结构是:

I want to build up a query which search dates on different entites. My structure is:

• 合同有日期(不可为空)
• 员工有日期(不可为空)
• 员工可能具有合同ID(可以为空)

如果某位员工有合同，我想获取合同日期.如果员工没有合同，那么我想返回员工日期.

If a Employee has a contract I want to retrieve the contract date. If an employee does not have a contract then I want to return the Employee date.

到目前为止，我的代码是:

My code so far is:

if (inputDate!= null) {
    ParameterExpression<Date> exp = criteriaBuilder.parameter(Date.class, "inputDate");
    criteria.add(criteriaBuilder.or(
        criteriaBuilder.isNull(employee.get("contract")),
        criteriaBuilder.lessThanOrEqualTo(employee.<Date>get("creationDate"), exp),   criteriaBuilder.lessThanOrEqualTo((employee.join("contract").<Date>get("fromDate")), exp) ));}

这似乎不起作用.我似乎总是会遇到意料之外的isNull.

This does not seem to work though. I always appear to go into the isNull which I do not expect.

我很乐意对此进行更多研究，但我想我的问题是这是否是正确的解决方法.是吗?我在criteriaBuilder中也看到了selectCase，所以也许这可能是一个更好的解决方案.

I am happy to look into this some more but I guess my question is whether this is the correct way of going about it. Is it? I have seen a selectCase as well in criteriaBuilder so perhaps that may be a better solution.

任何指针都将得到很好的接收.

Any pointers would be greatly received.

谢谢

推荐答案

这是一个解决方案，不确定是否可行，但是我们将在您的帮助下设法使其起作用:):

Here would be a solution, not sure if it works, but we will manage to get it work with your help :):

ParameterExpression<Date> inputDateExp = criteriaBuilder.parameter(Date.class, "inputDate");
Predicate employeeCreationDate = criteriaBuilder.lessThanOrEqualTo(
        employee.<Date>get("creationDate"), inputDateExp);
Predicate contractStartDate = criteriaBuilder.lessThanOrEqualTo(
        employee.join("contract").<Date>get("fromDate"), inputDateExp);

criteria.add(
        criteriaBuilder.selectCase().when(employee.get("contract").isNull(), employeeCreationDate).otherwise(contractStartDate));

我不明白为什么要使用"inputDate"作为表达式而不是日期?另外，我建议将criteria重命名为c，将criteriaBuilder重命名为cb，这样可以节省空间，并且我觉得更舒适.

I do not understand why use "inputDate" as Expression instead of a Date? Also, I suggest renaming criteria to c and criteriaBuilder to cb, this would save space and I think it is more comfortable.

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