如何使用 JPA Criteria Builder 编写带有附加计数列的查询

Question

我正在努力编写一个 JPA 查询，该查询将 return 数据库中的所有 P 对象，并且在它们旁边我想计算它们的 S 子对象的 propertyA = 1。

SQL查询

Select p.*, (Select count(s.id) 来自 s_table s 其中 p.id = s.p_id 和 s.propertyA = 1) 来自 p_table p

映射：

@Entity
@Table(name = "t_table")
public class PTable{
    @Id
    private String id;

    @Version
    private Long version;

    private String subject;
   
    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.EAGER)
    @JoinColumn(name = "p_id", referencedColumnName = "id")
    private Set<STable> sSet = new HashSet<>();
}
 
@Entity
@Table(name = "s_table")
public class STable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(name = "p_id")
    private String pId;
  
    private String propertyA;
}

此外，您是否愿意指出任何在 JPA 中编写复杂查询的好教程。

CriteriaBuilder cb = entityManager.getCriteriaBuilder();
CriteriaQuery<PTable> q = cb.createQuery(PTable.class);
Root<PTable> c = q.from(PTable.class);

Answer 1

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

Root<PTable> rootPTable = cq.from(PTable.class);
Join<PTable, STable> joinSTable = rootPTable.join(PTable_.sSet);

Subquery<Long> sqCount = cq.subquery(Long.class);
Root<STable> sqRootSTable = sqCount.from(STable.class);
Join<STable, PTable> sqJoinPTable = sqRootSTable.join(STable_.pSet);

sqCount.where(cb.and(
    cb.equal(sqJoinPTable.get(PTable_.id),rootPTable.get(PTable_.id)),
    cb.equal(sqRootSTable.get(STable_.propertyA),"1")));

sqCount.select(cb.count(sqRootSTable));

cq.multiselect(
    rootPTable.get(PTable_.id),
    rootPTable.get(PTable_.version),
    rootPTable.get(PTable_.subject),
    joinSTable.get(STable_.id),
    sqCount.getSelection(),
);

您将需要一个 Pojo 来获取构造函数具有的结果，该结果与多选参数的顺序和类型匹配，如下所示：

public MyPojo(String pId, Long version, String subject, Long sId, Long count){
    [...]
}

您还必须更改您的实体以正确映射关系，双向和懒惰以提高性能如下：

PTable

@OneToMany(mappedBy="p",fetch = FetchType.LAZY)
private Set<STable> sSet;

表

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name="id")
private PTable p;

如何使用 JPA Criteria Builder 编写带有附加计数列的查询

How to write query with additional count column using JPA Criteria Builder

hibernate

jpa

criteria-api

jpa-2.0