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

问题描述

我有一个使用JOIN和ORDER BY的查询，想要使用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，如何包装这样的查询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，我发现一些例子将Criteria Api与JpaRepository结合使用（< a href =http://www.cubrid.org/wiki_ngrinder/entry/how-to-create-dynamic-queries-in-springdata =nofollow>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一个规范：

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

T findOne(Specification<T> spec);

总是这样构建：

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));
        }
    };

}

所以在一方面我知道如何创建CriteriaQuery，另一方面，我需要一个基于谓词构建的规范，我无法弄清楚如何将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（我假设宠物有很多所有者）：

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);
            }
        };
    }

这只是搜索至少一位拥有者姓名的所有宠物的示例等于 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< Pet> findByOwnersNameOrderByIdDesc（String ownerName）; 在您的存储库中（相当于规范）。

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

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