JpaSpecificationExecutor JOIN + ORDER BY in 规范 [英] JpaSpecificationExecutor JOIN + ORDER BY in Specification

问题描述

我有一个使用 JOIN 和 ORDER BY 的查询，并希望使用 Criteria Api 在我的存储库中使用它.

I have a query using a JOIN and ORDER BY and want to use it within my repository using the Criteria Api.

在这里我发现，如何将这样的查询包装到 CriteriaQuery (链接).

Here I found, how to wrap such a query into a CriteriaQuery (Link).

CriteriaQuery<Pet> cq = cb.createQuery(Pet.class);
Root<Pet> pet = cq.from(Pet.class);
Join<Pet, Owner> owner = cq.join(Pet_.owners);
cq.select(pet);
cq.orderBy(cb.asc(owner.get(Owner_.lastName),owner.get(Owner_.firstName)));

另一方面，我找到了一些将 Criteria Api 与 JpaRepository 结合使用的示例(示例).

On the other side, I found some examples to use the Criteria Api in Combination with a JpaRepository (example).

问题是存储库中的所有方法都需要规范:

The Problem is that all methods in the repository expect a Specification:

T findOne(Specification<T> spec);

总是像这样构建:

public static Specification<PerfTest> statusSetEqual(final Status... statuses) {
    return new Specification<PerfTest>() {
        @Override

        public Predicate toPredicate(Root<PerfTest> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
            return cb.not(root.get("status").in((Object[]) statuses));
        }
    };

}

因此，一方面我知道如何创建 CriteriaQuery，另一方面我需要一个从谓词构建的规范，但我不知道如何将 CriteriaQuery 解析为规范/谓词.

So at one side I know how to create a CriteriaQuery, and on the other side I need a Specification which is build from a Predicate, and I can not figure out how to parse the CriteriaQuery into a Specification/Predicate.

推荐答案

尝试这样的事情(我假设宠物有很多主人):

Try something like this (I assumed pet has many owners):

public static Specification<Pet> ownerNameEqual(String ownerName) {
        return new Specification<Pet>() {
            @Override
            public Predicate toPredicate(Root<Pet> root, CriteriaQuery<?> criteriaQuery, CriteriaBuilder criteriaBuilder) {
                Join<Pet, Owner> owners = root.join("owners");
                criteriaQuery.orderBy(criteriaBuilder.desc(root.get("id")));
                return criteriaBuilder.equal(owners.get("name"), ownerName);
            }
        };
    }

这只是一个搜索所有宠物的例子，其中至少有一个主人的名字等于ownerName

This is just an example to search all pets whose at least one owner has name equal to ownerName

但是你可以添加一个方法 List;findByOwnersNameOrderByIdDesc(String ownerName); 改为在您的存储库中(相当于 Specification).

But you could add a method List<Pet> findByOwnersNameOrderByIdDesc(String ownerName); in your repository instead (as an equivalent to Specification).

这篇关于JpaSpecificationExecutor JOIN + ORDER BY in 规范的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！