Java JpaSpecificationExecutor JOIN + ORDER BY in Specification
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JpaSpecificationExecutor JOIN + ORDER BY in Specification
提问by aschi
I have a query using a JOIN and ORDER BY and want to use it within my repository using the Criteria Api.
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。
Here I found, how to wrap such a query into a CriteriaQuery (Link).
在这里我发现，如何将这样的查询包装到 CriteriaQuery ( Link) 中。
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)));
On the other side, I found some examples to use the Criteria Api in Combination with a JpaRepository (example).
另一方面，我找到了一些将 Criteria Api 与 JpaRepository 结合使用的示例（示例）。
The Problem is that all methods in the repository expect a Specification:
问题是存储库中的所有方法都需要规范：
T findOne(Specification<T> spec);
which is always build like this:
它总是像这样构建：
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));
}
};
}
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.
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，我不知道如何将 CriteriaQuery 解析为规范/谓词。
采纳答案by Jakub Bibro
Try something like this (I assumed pet has many owners):
尝试这样的事情（我假设宠物有很多主人）：
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);
}
};
}
This is just an example to search all pets whose at least one owner has name equal to ownerName
这只是一个示例，用于搜索至少一个主人的名字等于ownerName 的所有宠物
But you could add a method List<Pet> findByOwnersNameOrderByIdDesc(String ownerName);in your repository instead (as an equivalent to Specification).
但是您可以List<Pet> findByOwnersNameOrderByIdDesc(String ownerName);改为在您的存储库中添加一个方法（相当于规范）。
