加入JPA彈簧數據規範

Question

我已經創建了一些org.springframework.data.jpa.domain.Specifications。現在我正在創建一個查詢，在該查詢中我想使用我加入的表上的規範。但是爲了使用規範，我需要一個Root，但是連接給了我一個Join對象。

有沒有從Join對象轉換爲Root的方法？或者有沒有類似於規範的東西，但對於聯接？

Answer 1

Tarwirdur Turon的解決方案不適合我的需要，所以我設法創建一個Root<T>把一個Join成Root將所有方法委託給一個Join<?,T>實例的實現。 （Join和Root是From的子接口） 儘管它起作用，但它對我來說看起來很髒。因爲我有一個已經建成Specification<JoinedEntity>，我想找到該joinedEntity不知道什麼是「內部」本說明書中的規格相匹配的所有Entity

Tarwirdur Turon的解決方案並不爲我工作。

public class JoinRoot<T> implements Root<T> { 
    private final Join<?, T> join; 
    public JoinRoot(Join<?, T> join) { 
     this.join = join; 
    } 

    // implements all Root methods, delegating them to 'this.join' (#boilerplate), 
    // cast when needed 

    @Override 
    public EntityType<T> getModel() { 
     // this one is the only one that cannot be delegated, although it's not used in my use case 
     throw new UnsupportedOperationException("getModel cannot be delegated to a JoinRoot"); 
    } 
} 

然後使用這個類像如下：

Specification<JoinedEntity> joinedSpecs = ... 

Specification<Entity> specs = (root, query, builder) -> { 
    // Convert Join into Root using above JoinRoot class 
    Root<JoinedEntity> r = new JoinRoot<>(root.join(Entity_.joinedEntity)); 
    return joinedSpecs.toPredicate(r, query, builder); 
} 
Specification<Entity> where = Specifications.where(specs); 

List<Entity> entities = entityRepository.findAll(where); 

我真的不知道爲什麼Specification.toPredicate方法採用Root<X>作爲第一個參數，而不是From<Z,X>，這將緩解所有的事情...

Answer 2

您不需要Root對象。 Join對象是Path和Expression接口的實例。見與工作示例從規格加入：

class JoinedSpecification extends Specification<JoinedEntity>() { 
    public Predicate pathPredicate(Path<JoinedEntity> joinedEntity, CriteriaQuery<?> query, CriteriaBuilder builder) { 
     return builder.equal(joinedEnity.get(JoinedEntity_.value), 20L); 
    } 

    @Override 
    public Predicate toPredicate(Root<JoinedEntity> root, CriteriaQuery<?> query, CriteriaBuilder builder) { 
     return pathPredicate(root, query, builder); 
    } 
} 

class MySpecification extends Specification<Entity>() { 
    private static JoinedSpecification joinedSpecification = new JoinedSpecification(); 

    @Override 
    public Predicate toPredicate(Root<Entity> root, CriteriaQuery<?> query, CriteriaBuilder builder) { 
     Join<T, JoinedEntity> join = root.join(Entity_.joinedEntity, JoinType.LEFT); 

     // Some join condition 
     Path<Long> someExpr = join.get(JoinedEntity_.someExpr); 
     Long someExprCriteria = 10L; 
     join = join.on(builder.equal(someExpr, someExprCriteria)); 

     return joinedSpecification.pathPredicate(join, query, builder); 
    } 
} 

@Autowired 
JpaSpecififcationExecutor<Entity> service; 

Specification<Entity> spec = new MySpecification(); 
serivce.findAll(spec); 

它將提供查詢像

SELECT e FROM Entity e LEFT JOIN e.joinedEntity j WITH j.someExpr=10 WHERE j.value = 20;