多对多 - select 没有确定字段且结果数量有限的实体集合

Question

我有两个实体class存在多对多关系

@Entity
public class User implements Serializable {
    ...

    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.ALL, mappedBy = "members")
    private Set<Group> groups = new HashSet<>();

}

和

@Entity
public class Group implements Serializable {
  ...

  @JoinTable(name = "user_groups",
          joinColumns = {@JoinColumn(name = "group_id")},
          inverseJoinColumns = {@JoinColumn(name = "user_id")})

  private Set<User> members = new HashSet<>();

}

当我请求获取特定组时，我得到：

{
  "id": 12,
  "adminId": 12345,
  "name": "name",
  "category": "cat",
  "city": "city",
  "members": [
    { 
      "id": 1,
      "firstName": "SomeName",
      "birthday": 802476000000,
      "city": "SomeCity",
      "country": "SomeCountry",
      "age": 21,
      "groups": [
        {
          "id": 1,
          "adminId": 123,
          "name": "Some group name",
          "category": "some category",
          "city": "some city"
        }
      ],
      "picturePath": some path
    }
]

} 当我想通过 id 获取特定组时，在其成员字段中，我只想拥有没有组字段的用户和数据库中的前 100 行。希望您理解：用户属于多个组，组有多个用户

我想要这样的东西：

{
  "id": 12,
  "adminId": 12345,
  "name": "name",
  "category": "cat",
  "city": "city",
  "members": [
    { 
      "id": 1,
      "firstName": "SomeName",
      "birthday": 802476000000,
      "city": "SomeCity",
      "country": "SomeCountry",
      "age": 21,
      "picturePath": some path
    }
]

我想到的是创建和连接 table 的实体 class（其中包含列：user_id、group_id）并创建将获得的查询给定 group_id 的 user_id 的结果，然后在循环中让用户获得我感兴趣的字段

也许我应该使用一些元组查询？感谢您花时间解决我的问题

Answer 1

哦，愚蠢的我:)

Query query = entityManager.createNativeQuery("SELECT u.user_id,u.birthdate,u.first_name,u.city,u.country,u.age,u.picture_path " +
                "FROM users u " +
                "INNER JOIN user_groups ug " +
                "ON ug.user_id = u.user_id WHERE ug.group_id = ?",User.class);

user_groups 是一个连接 table，可以使用 LIMIT 来计算结果（在 MySQL 中）

多对多 - select 没有确定字段且结果数量有限的实体集合

Many to many - select collection of entities without determined field and with limited number of results

java

mysql

many-to-many

hibernate

jpa