@JoinTable 的 JPA 查询

Question

场景： 我有两个实体用户和程序

@Entity
@Table(name = "user")
public class UserEntity implements Serializable{

   @Id
   public Long id;

   public String firstName;

   public String email;

   @OneToOne(cascade = CascadeType.ALL)
   @JoinTable(
      name = "user_program",
      joinColumns = {
         @JoinColumn(name = "user_id", referencedColumnName = "id")  
      },
      inverseJoinColumns = {
         @JoinColumn(name = "program_id", referencedColumnName = "id")
      }
   )
   public ProgramEntity program;
}

JPQL：

SELECT
   Program.name,
   COUNT(user.id) AS user_count
FROM UserEntity AS user
INNER JOIN ProgramEntity AS program on ________ GROUP BY Program.name

我尝试获取每个程序中的用户数，但由于JoinTable（中间表）不是实体，我无法获得结果。谁能建议一个 JPQ 来连接连接表？

Answer 1

您可以使用实体对象加入，“ON”不是必需的。以你为例，

SELECT prg.name, COUNT(user.id) AS user_count FROM UserEntity AS user INNER JOIN user.program AS prg GROUP BY prg.name