本文介紹了MyBatis中的一對多關系的處理方法，對大家解決問題具有一定的參考價值，需要的朋友們下面隨著小編來一起學習吧！
問題描述
我正在嘗試使用MyBatis在我的數據模型中映射一對多關系。這基于以下類：
class Team{
String mId;
String mName;
List<Player> mPlayers;
}
class Player{
String mId;
String mName;
}
我想編寫一個返回匹配列表的查詢，每個匹配列表都填充了與該匹配對應的標記。
<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>
但我遇到的問題是，每個Team對象只填充了一個球員。如何更改此設置以確保每支球隊都包含屬于它的所有球員？
推薦答案
我試圖回答這個問題，并使用注釋在Mybatis中創建了一對多關系。以下是我的代碼
UserMapper.java
@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);
我的Team.java：
public class Team {
private Long teamId;
private String name;
private List<Player> players;
//...getters and setters
}
Player.java：
public class Player {
private Long playerId;
private String name;
private Team team;
//...getter and setters
}
Team.sql
CREATE TABLE `team` (
`teamId` bigint(10) NOT NULL AUTO_INCREMENT,
`name` varchar(50) DEFAULT NULL,
PRIMARY KEY (`teamId`)
)
player.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
@Autowired
private UserMapper userMapper;
...
/* Get the list of teams with players data */
List<Team> teams = userMapper.getAllTeams();
...
希望本文對未來的讀者有所幫助。
這篇關于MyBatis中的一對多關系的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，
