具有多个参数的JPA Criteria API

Question

我需要创建一个使用带有多个参数的JPA Criteria API的搜索方法.现在的问题是不是每个参数都是必需的.因此有些可能为null,并且它们不应包含在查询中.我已经用CriteriaBuilder尝试了这个,但我看不出如何让它工作.

使用Hibernate Criteria API,这非常简单.只需创建条件,然后添加限制.

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

我怎么能用JPA的Criteria API实现同样的目标？

Answer 1

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

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();

Answer 2

Spring 的一个简单解决方案，使用 lambda 表达式：

Specification<User> specification = (root, query, builder) -> {
    List<Predicate> predicates = new ArrayList<>();

    // like
    predicates.add(builder.like(root.get("name"), "%test%"));

    // equal
    predicates.add(builder.equal(root.get("parent_id"), 99L);


    // AND all predicates
    return builder.and(predicates.toArray(new Predicate[0]));
};

repository.findAll(specification);

Answer 3

看看这个网站JPA Criteria API.有很多例子.

更新:提供一个具体的例子

让我们搜索余额低于特定值的帐户:

SELECT a FROM Account a WHERE a.balance < :value

首先创建一个Criteria Builder

CriteriaBuilder builder = entityManager.getCriteriaBuilder();

CriteriaQuery<Account> accountQuery = builder.createQuery(Account.class);
Root<Account> accountRoot = accountQuery.from(Account.class);
ParameterExpression<Double> value = builder.parameter(Double.class);
accountQuery.select(accountRoot).where(builder.lt(accountRoot.get("balance"), value));

要获取结果集参数并运行查询:

TypedQuery<Account> query = entityManager.createQuery(accountQuery);
query.setParameter(value, 1234.5);
List<Account> results = query.getResultList();

BTW:entityManager被注入EJB/Service/DAO中的某个地方.