如何使用mybatis映射JSON_ARRAYAGG结果

Question

我无法映射来自JSON_ARRAYAGG function的结果。

mybatis mapper：

<mapper namespace="com.test.mapper.UserEntityMapper">
    <resultMap id="userMap" type="UserVO">
        <id property="id" column="id" />
        <result property="username" column="username"/>
        <collection property="pictures" ofType="PictureVO">
            <id property="id" column="id" />
            <result property="location" column="location" />
        </collection>
    </resultMap>
    <select id="findUserById" parameterType="map" resultMap="userMap">
        SELECT
        users.id,
        users.username,
        JSON_ARRAYAGG(
            JSON_OBJECT(
                "id",
                pic.id,
                "location",
                pic.location
            ) 
        ) AS pictures
        FROM
            users
            LEFT JOIN pictures pic ON users.id = pic.user_id 
        WHERE
            users.id = 1
    </select>
</mapper>

UserVO型号：

@Getter
@Setter
@NoArgsConstructor
public class UserVO {
    private Long id;
    private String username;
    private List<PictureVO> pictures;
}

PictureVO型号：

@Getter
@Setter
@NoArgsConstructor
public class PictureVO {
    private Long id;
    private String location;
}

调用API的结果如下：

{
    "id": 1,
    "username": "connor",
    "pictures": [
        {
            "id": 1,
            "location": null
        }
    ]
}

如您所见，只有id才能正确映射pictures。假设在pictures中有2个结果，如果我直接执行sql，这里只返回1个结果。

Answer 1

你应该设置你的方法的("findUserById")返回类型列表，MyBatis会自动完成。尝试在mapper接口中编写它：

List<UserVo> findUserById();

Answer 2

MyBatis返回的是Java对象，而不是JSON，所以可能是您的'API‘将Java对象转换为JSON。

如果我是对的，你只需要做正常的MyBatis映射。

如下所示：

<resultMap id="userMap" type="UserVO">
  <id property="id" column="id" />
  <result property="username" column="username"/>
  <collection property="pictures" ofType="PictureVO">
    <id property="id" column="picture_id" />
    <result property="location" column="location" />
  </collection>
</resultMap>

<select id="findUserById" parameterType="map" resultMap="userMap">
  SELECT
    users.id,
    users.username,
    pic.id picture_id,
    pic.location
  FROM
    users
    LEFT JOIN pictures pic ON users.id = pic.user_id
  WHERE
    users.id = 1
</select>

请注意，pic.id需要一个别名来区分结果集中的列和users.id。