具有多个参数的 JPA Criteria API [英] JPA Criteria API with multiple parameters

问题描述

我需要创建一个使用带有多个参数的 JPA Criteria API 的搜索方法.现在的问题是并不是每个参数都是必需的.所以有些可能为空，它们不应该包含在查询中.我已经用 CriteriaBuilder 试过了，但我不知道如何让它工作.

I need to make a search method that uses the JPA Criteria API with multiple parameters. Now the problem is that not every parameter is required. So some could be null, and they shouldn't be included in the query. I've tried this with the CriteriaBuilder but I couldn't see how to make it work.

使用 Hibernate Criteria API，这相当容易.只需创建条件，然后添加限制即可.

With the Hibernate Criteria API this is fairly easy. Just create the criteria and then add Restrictions.

Criteria criteria = session.createCriteria(someClass.class);
if(someClass.getName() != null) {
   criteria.add(Restrictions.like("name", someClass.getName());
}

如何使用 JPA 的 Criteria API 实现相同的目标?

How could I achieve the same with JPA's Criteria API?

推荐答案

概念是构造javax.persistence.Predicate 只包含我们想要使用的谓词:

Concept is to construct array of javax.persistence.Predicate which contains only predicates we want to use:

要查询的示例实体:

@Entity
public class A {
    @Id private Long id;    
    String someAttribute;
    String someOtherAttribute;
    ...
}

查询本身:

    //some parameters to your method
    String param1 = "1";
    String paramNull = null;

    CriteriaBuilder qb = em.getCriteriaBuilder();
    CriteriaQuery cq = qb.createQuery();
    Root<A> customer = cq.from(A.class);

    //Constructing list of parameters
    List<Predicate> predicates = new ArrayList<Predicate>();

    //Adding predicates in case of parameter not being null
    if (param1 != null) {
        predicates.add(
                qb.equal(customer.get("someAttribute"), param1));
    }
    if (paramNull != null) {
        predicates.add(
                qb.equal(customer.get("someOtherAttribute"), paramNull));
    }
    //query itself
    cq.select(customer)
            .where(predicates.toArray(new Predicate[]{}));
    //execute query and do something with result
    em.createQuery(cq).getResultList();

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