JpaSpecificationExecutor JOIN + ORDER BY in Specification

问题:

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

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))); 

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

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

T findOne(Specification<T> spec); 

which is always build like this:

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.

回答1:

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);             }         };     } 

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

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

文章来源: JpaSpecificationExecutor JOIN + ORDER BY in Specification