JPA 2 标准多对多子选择

Question

I have the following scenario:

Person.class:

@Entity
@Table(name = "person")
@SequenceGenerator(name = "seq_person", sequenceName = "seq_person", allocationSize = 1, initialValue = 1)
public class Person implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_pessoa")
    @Column(name = "id")
    private int id;

    @Column(name = "name", nullable = false)
    private String name;

    @ManyToMany(fetch = FetchType.LAZY, cascade = { javax.persistence.CascadeType.REFRESH, javax.persistence.CascadeType.MERGE })
    @JoinTable(name = "person_category", joinColumns = { @JoinColumn(name = "person_id") }, inverseJoinColumns = { @JoinColumn(name = "category_id") })
    protected List<Category> categories = new ArrayList<>();

    ...
}

Category.class:

@Entity
@Table(name = "category")
@SequenceGenerator(name = "seq_category", sequenceName = "seq_category", allocationSize = 1, initialValue = 1)
public class Category implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "seq_category")
    @Column(name = "id")
    private int id;

    @Column(name = "name", nullable = false)
    private String name;

    ...
}

With this scenario, I need to do a query using JPA2 Criteria, to substitute this HQL query:

SELECT obj FROM Person AS obj
WHERE EXISTS (
    SELECT category.id FROM obj.categories AS category
    WHERE category.name = 'Staff'
)

I've tried to make a join with categories, but it multiply the result by the quantity of categories of each person:

CriteriaBuilder cb = this.entityManager.getCriteriaBuilder();
CriteriaQuery<Person> cq = cb.createQuery(Person.class);

Root<Person> root = cq.from(Person);

cq.select(root);

Subquery<Category> subquery = cq.subquery(Category.class);
Root<Category> subqueryFrom = subquery.from(Category.class);
subquery.select(subquery.from(clazz).get("id"));

Predicate predicateJoin = cb.equal(root.join("categories", JoinType.LEFT), subqueryFrom);
Predicate predicateName = cb.like(subqueryFrom.get("name"), "%" + content + "%");

subquery.where(cb.and(predicateJoin, predicateName));
cb.where(cb.exists(subquery));

TypedQuery<Person> typedQuery = this.entityManager.createQuery(cq);

List<Person> resultList = typedQuery.getResultList();

This criteria result in this SQL:

select
    person0_.id as id1_50_,
    person0_.name as name29_50_
from
    person person0_ 
left outer join
    person_category categories2_ 
        on person0_.id=categories2_.person_id 
left outer join
    category categoryp3_ 
        on categories2_.category_id=categoryp3_.id 
where
    exists (
        select
            categoryp5_.id 
        from
            person_category categoryp4_ cross 
        join
            person_category categoryp5_ 
        where
            categoryp3_.id=categoryp4_.id 
            and (
                categoryp4_.name like ?
            )
    )

The generated SQL do a CROSS JOIN with person_category and do the LEFT JOIN out of subselect.

Using the HQL Hibernate produces the following SQL:

select
    person0_.id as id1_50_,
    person0_.name as name29_50_
from
    person person0_ 
where
    exists (
        select
            categoryp2_.id 
        from
            person_category categories1_,
            category categoryp2_ 
        where
            person0_.id=categories1_.person_id 
            and categories1_.category_id=categoryp2_.id 
            and categoryp2_.name=?
    )

How I can do this query in Criteria?

Answer 1

You need to correlate() the outer query with the subquery. Try something along the following lines (it is hard to test without having the real model, but should be close enough):

    CriteriaBuilder cb = this.entityManager.getCriteriaBuilder();
    CriteriaQuery<Person> cq = cb.createQuery(Person.class);

    Root<Person> root = cq.from(Person.class);

    cq.select(root);

    Subquery<Category> subquery = cq.subquery(Category.class);
    Root<Person> subqueryRoot = subquery.correlate(root);
    Join<Person,Category> personCategories = subqueryRoot.join("categories");
    subquery
        .select(personCategories) // check out comment for possible needed change
        .where(cb.equal(personCategories.get("name"), "Staff"));
    
    cq.where(cb.exists(subquery));

    TypedQuery<Person> typedQuery = this.entityManager.createQuery(cq);

    List<Person> resultList = typedQuery.getResultList();

This should result in:

SELECT obj FROM Person AS obj
WHERE EXISTS (
    SELECT category FROM obj.categories AS category
    WHERE category.name = 'Staff'
)