Loopback4 中包含记录的限制答案

【问题标题】：Limit for included records in Loopback4Loopback4 中包含记录的限制
【发布时间】：2021-03-21 00:25:01
【问题描述】：

我想查询运动模型对象并包含相关对象（关系：athletExerciseLogsExercise）。但我只需要 1 个相关对象，这就是为什么我将“限制：1”添加到包含范围：

exerciseController.find({
    include: [{
        relation: "athletExerciseLogsExercise",
        scope: {
            where: {
                userId: id
            },
            order: ['date DESC'],
            limit: 1
        }
    }, ]
});

型号

export class Exercise extends Entity {
  ...
  @hasMany(() => AthletExerciseLog, {keyTo: 'exerciseId'})
  athletExerciseLogsExercise?: AthletExerciseLog[];
  ...
}

SQL（来自调试）

SELECT
  "id",
  "userid",
  "exerciseid",
  "date"
  ...
FROM
  "public"."athletexerciselog"
WHERE
  "userid" = '65b9b7110230'
  AND "exerciseid" IN (
    'd67503d511bb',
    '46d156a58aee'
  )
ORDER BY  "date" DESC
LIMIT 1

问题：SQL 结果只包含 1 条记录 for one "exerciseid" = 'd67503d511bb'

问题：如何从“athletexerciselog”为每个“exerciseid”接收1条记录？

【问题讨论】：

标签： strongloop loopback loopback4

【解决方案1】：

我找到了以下解决方案，这可能是开销，但我找不到其他方法...

1 - 创建数据库视图：为每个 userid 和 exerciseid

仅选择 1 个（最后一个）记录

CREATE VIEW "v_athletexerciselog" AS  
  SELECT q.*
  FROM athletexerciselog q
  WHERE (
        q.id IN ( 
          SELECT max(i.id) AS max
           FROM athletexerciselog i
          WHERE (i.event IS NULL)
          GROUP BY i.userid, i.exerciseid
        )
  )

2 - 创建一个新的 LB4 模型和存储库 使用自定义表名（视图名）扩展原始模型

@model({
  settings: {
    postgresql: {schema: 'public', table: 'v_athletexerciselog'}, // custom names
  },
})
export class VAthletExerciseLog extends AthletExerciseLog {
  constructor(data?: Partial<VAthletExerciseLog>) {
    super(data);
  }
}

3 - 将运动模型和存储库中的相关模型名称更改为 VAthletExerciseLog（新）

export class Exercise extends Entity {
  ...
  @hasMany(() => VAthletExerciseLog, {keyTo: 'exerciseId'})
  athletExerciseLogsExercise?: VAthletExerciseLog[];
  ...
}

4 - 从查询中删除“订单”和“限制”：

exercise.find({
    include: [{
        relation: "athletExerciseLogsExercise",
        scope: {
            where: {
                userId: id
            },
            //order: ['date DESC'],
            //limit: 1
        }
    }, ]
});

【讨论】：