JPQL 按子列计数多个多对一和组计数

Question

我想构建一个 JPQL 查询来将该结构的数据映射到这个 DTO：

@AllArgsConstructor
class UserDTO {
  long userId;
  long countOfContacts;
  Map<String,Long> countOfActions; // by type
}

我不知道如何在 JPQL 中提取每个动作类型的计数，这就是我卡住的地方（看到我的名字了吗？:)）：

public interface UserRepository extends CrudRepository<User, Long> {
    @Query("SELECT new example.UserDTO( "
            + "   u.id, "
            + "   COUNT(contacts), "
        --> + "   ???group by actions.type to map<type,count>??? " <---
            + " ) "
            + " FROM User u "
            + " LEFT JOIN u.actions actions "
            + " LEFT JOIN u.contacts contacts "
            + " GROUP BY u.id")
    List<UserDTO> getAll();
}

我使用 postgres，如果这在 JPQL 中是不可能的，我也可以使用本机查询。

其实我可以通过原生查询和Java中的actions数据映射来解决，但是感觉很糟糕：

SELECT
  u.id,
  COALESCE(MIN(countOfContacts.count), 0) as countOfContacts,
  ARRAY_TO_STRING(ARRAY_REMOVE(ARRAY_AGG(actions.type || ':' || actions.count), null),',') AS countOfActions
FROM user u
LEFT JOIN (
    SELECT
      user_id, COUNT(*) as count
    FROM contact
    GROUP BY user_id
) countOfContacts
  ON countOfContacts.user_id = u.id
LEFT JOIN (
    SELECT
      user_id, type, COUNT(*)
    FROM action
    GROUP BY user_id, type
) actions
  ON actions.user_id = u.id
GROUP BY u.id
;

产生这样的结果数据：

  id   | countOfContacts |     countOfActions                            
--------+-----------------+-------------------------
 11728 |               0 | {RESTART:2}
  9550 |               0 | {}
  9520 |               0 | {CLEAR:1}
 12513 |               0 | {RESTART:2}
 10238 |               3 | {CLEAR:2,RESTART:5}
 16531 |               0 | {CLEAR:1,RESTART:7}
  9542 |               0 | {}
...

由于在原生查询中我们无法映射到 POJO，所以我返回 List<String[]> 并自行将所有列转换为 UserDTO 的构造函数：

@Query(/*...*/)
/** use getAllAsDTO for a typed result set */
List<String[]> getAll();

default List<UserDTO> getAllAsDTO() {
  List<String[]> result = getAll();
  List<UserDTO> transformed = new ArrayList<>(result.size());
  for (String[] row : result) {
    long userId = Long.parseLong(row[0]);
    long countOfContacts = Long.parseLong(row[1]);
    String countOfActions = row[2];
    transformed.add(
      new UserDTO(userId, countOfContacts, countOfActions)
    );
  }
  return transformed;
}

然后我在 DTO 的构造函数中将 countOfActions 映射到 Java Map<String, Long>：

    class UserDTO {
        long userId;
        long countOfContacts;
        Map<String,Long> countOfActions; // by type

        /**
         * @param user
         * @param countOfContacts
         * @param countOfActions {A:1,B:4,C:2,..} will not include keys for 0
         */
        public UserDTO(long userId, long countOfContacts, String countOfActionsStr) {
            this.userId = userId;
            this.countOfContacts = countOfContacts;
            this.countOfActions = new HashMap<>();
            // remove curly braces
            String s = countOfActionsStr.replaceAll("^\\{|\\}$", "");
            if (s.length() > 0) { // exclude empty "arrays"
              for (String item : s.split(",")) {
                  String[] tmp = item.split(":");
                  String action = tmp[0];
                  long count = Long.parseLong(tmp[1]);
                  countOfActions.put(action, count);
              }
            }
        }
    }

我已经可以在 DB 层解决了吗？

Answer 1

很遗憾，JPQL 没有像 string_agg 或 group_concat 这样的聚合函数。所以你应该自己转换查询结果。首先，您应该像这样创建一个“普通”查询，例如：

@Query("select new example.UserPlainDto( " + 
       "  a.user.id, " +
       "  count(distinct c.id), " +
       "  a.type, " +
       "  count(distinct a.id) " +
       ") " +
       "from " +
       "  Action a " +
       "  join Contact c on c.user.id = a.user.id " +
       "group by " +
       "  a.user.id, a.type")
List<UserPlainDto> getUserPlainDtos();

（它是HQL - JPQL 的 Hibernate 扩展）

这个查询的结果将是一个普通的表，例如：

|--------|---------------|-------------|-------------|
|user_id |countact_count |action_type  |action_count |
|--------|---------------|-------------|-------------|
|1       |3              |ONE          |1            |
|1       |3              |TWO          |2            |
|1       |3              |THREE        |3            |
|2       |2              |ONE          |1            |
|2       |2              |TWO          |2            |
|3       |1              |ONE          |1            |
|--------|---------------|-------------|-------------|

然后你应该将该结果分组到UserDto 的集合中，如下所示：

default Collection<UserDto> getReport() {
    Map<Long, UserDto> result = new HashMap<>();

    getUserPlainDtos().forEach(dto -> {
        long userId = dto.getUserId();
        long actionCount = dto.getActionCount();

        UserDto userDto = result.getOrDefault(userId, new UserDto());
        userDto.setUserId(userId);
        userDto.setContactCount(dto.getContactCount());
        userDto.getActions().compute(dto.getActionType(), (type, count) -> count != null ? count + actionCount : actionCount);
        result.put(userId, userDto);
    });

    return result.values();
}

然后瞧，你会在Collection<UserDto>得到这样的结果：

[
    {
        "userId": 1,
        "contactCount": 3,
        "actions": {
            "ONE": 1,
            "TWO": 2,
            "THREE": 3
        }
    },
    {
        "userId": 2,
        "contactCount": 2,
        "actions": {
            "ONE": 1,
            "TWO": 2
        }
    },
    {
        "userId": 3,
        "contactCount": 1,
        "actions": {
            "ONE": 1
        }
    }
]

上面使用了DTO：

@Value
class UserPlainDto {
    long userId;
    long contactCount;
    ActionType actionType;
    long actionCount;
}

@Data
class UserDto {
    long userId;
    long contactCount;
    Map<ActionType, Long> actions = new HashMap<>();
}

My demo project.