java MyBatis 中的一对多关系
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One to many relationship in MyBatis
提问by spacitron
I'm trying to use MyBatis to map a one to many relationship in my data model. This is based on the following classes:
我正在尝试使用 MyBatis 在我的数据模型中映射一对多关系。这是基于以下类：
class Team{
String mId;
String mName;
List<Player> mPlayers;
}
class Player{
String mId;
String mName;
}
I would like to write a query that returns a list of matches, each populated with the tags that correspond to that match.
我想编写一个返回匹配列表的查询，每个匹配都填充了与该匹配对应的标签。
<select id="getTeams" resultType="Team" resultMap="TeamMap">
SELECT id, name, players.id as player_id, players.name as player_name
FROM teams
JOIN players ON teams.id = players.team_id
</select>
<resultMap type="Team" id="TeamMap">
<id property="mId" column="id"/>
<result property="mName" column="name"/>
<collection property="mTags" javaType="List" ofType="Player">
<id property="player_id" column="mId"/>
<result property="player_name" column="mName"/>
</collection>
</resultMap>
But the problem I'm having with this is that each Team object is only populated with a single Player. How can I change this to ensure that each team contains all players that belong to it?
但是我遇到的问题是每个 Team 对象只填充了一个 Player。如何更改此设置以确保每个团队都包含属于它的所有玩家？
回答by Lucky
I've tried to follow this question and I've created a One-to-Many relationship in Mybatis using Annotations. Following is my code,
我试图遵循这个问题，并使用注释在 Mybatis 中创建了一对多关系。以下是我的代码，
UserMapper.java
用户映射器
@Select("SELECT teamId, name FROM TEAM")
@Results(value = {
@Result(property="teamId", column = "teamId"),
@Result(property="name", column = "name"),
@Result(property="players", column="teamId", javaType= List.class, many=@Many(select="selectPlayers"))
})
public List<Team> getAllTeams();
@Select("SELECT * FROM PLAYER WHERE teamId = #{teamId}")
@Results(value={
@Result(property="playerId", column ="playerId" ),
@Result(property="name", column = "name")
})
List<Player> selectPlayers(String teamId);
My Team.java:
我的Team.java：
public class Team {
private Long teamId;
private String name;
private List<Player> players;
//...getters and setters
}
Player.java:
播放器.java:
public class Player {
private Long playerId;
private String name;
private Team team;
//...getter and setters
}
team.sql
团队.sql
CREATE TABLE `team` (
`teamId` bigint(10) NOT NULL AUTO_INCREMENT,
`name` varchar(50) DEFAULT NULL,
PRIMARY KEY (`teamId`)
)
player.sql
播放器.sql
CREATE TABLE `player` (
`playerId` bigint(10) NOT NULL AUTO_INCREMENT,
`name` varchar(50) DEFAULT NULL,
`teamId` bigint(10) DEFAULT NULL,
PRIMARY KEY (`playerId`),
KEY `FK_TEAM_ID` (`teamId`),
CONSTRAINT `FK_TEAM_ID` FOREIGN KEY (`teamId`) REFERENCES `team` (`teamId`)
)
UserServiceImpl.java
UserServiceImpl.java
@Autowired
private UserMapper userMapper;
...
/* Get the list of teams with players data */
List<Team> teams = userMapper.getAllTeams();
...
Hope this serves useful for future readers.
希望这对未来的读者有用。
回答by spacitron
Found the solution. All I had to do was change the player_id mapping in the collection from "id" to "result".
找到了解决办法。我所要做的就是将集合中的 player_id 映射从“id”更改为“result”。
