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MyBatisPlus中Join聯(lián)表查詢的項(xiàng)目實(shí)踐

更新時(shí)間：2026年04月02日 10:35:58 作者：小徐敲java

MyBatis-Plus本身并不直接支持JOIN連表查詢,可以通過自定義SQL或者使用MyBatis的原生XML配置來實(shí)現(xiàn)JOIN連表查詢,本文就來介紹一下MyBatisPlus中Join聯(lián)表查詢的項(xiàng)目實(shí)踐,感興趣的可以了解一下

4-1：User 實(shí)體類
4-2：Address 實(shí)體類
4-3：UserDTO 數(shù)據(jù)傳輸對(duì)象
4-4：userMapper代碼查詢
4-5：生成的SQL語句，基于MPJLambdaWrapper代碼，MyBatis-Plus-Join會(huì)生成如下SQL：
4-6：執(zhí)行結(jié)果生成sql處理，MyBatis-Plus-Join會(huì)自動(dòng)處理結(jié)果集，將數(shù)據(jù)映射為：

注意

MyBatis-Plus-Join官網(wǎng)

1：添加依賴

<dependency>
    <groupId>com.github.yulichang</groupId>
    <artifactId>mybatis-plus-join-boot-starter</artifactId>
    <version>1.5.3</version>
</dependency>
<!-- 對(duì)于的mybaits-plus版本 -->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.5.9</version>
</dependency>

2：原來寫法的Mapper類，繼承BaseMapper（其他全部不用修改）

@Mapper
public interface UserMapper extends BaseMapper<User> {
}

2-1：修改為的繼承MPJBaseMapper

@Mapper
public interface UserMapper extends MPJBaseMapper<User> {
}

3：例子

MPJLambdaWrapper<DoorControllerSettingsDoorInfoDO> doorControllerSettingsDoorInfoDOMPJLambdaWrapper = new MPJLambdaWrapper<DoorControllerSettingsDoorInfoDO>()
        .selectAll()
        .leftJoin(DoorControllerSettingsDO.class, DoorControllerSettingsDO::getControllerNumber, DoorControllerSettingsDO::getControllerNumber);
doorControllerSettingsMapper.selectJoinList(DoorControllerSettingsDO2.class, doorControllerSettingsDO2MPJLambdaWrapper);

4：對(duì)于selectCollection和selectAssociation的使用

4-1：User 實(shí)體類

@Data
@TableName("user")
public class User {
    @TableId
    private Long id;
    private String username;
    private String password;
    private Integer age;
    private String email;
}

4-2：Address 實(shí)體類

@Data
@TableName("address")
public class Address {
    @TableId
    private Long id;
    private Long userId;  // 外鍵，關(guān)聯(lián)user.id
    private String province;
    private String city;
    private String district;
    private String detail;
}

4-3：UserDTO 數(shù)據(jù)傳輸對(duì)象

@Data
public class UserDTO {
    private Long id;
    private String username;
    private String password;
    private Integer age;
    private String email;
    // 使用List接收一對(duì)多關(guān)系
    private List<Address> addressList;
}

4-4：userMapper代碼查詢

MPJLambdaWrapper<User> wrapper = new MPJLambdaWrapper<User>()
                .selectAll(User.class)
                //全部映射 不用考慮字段名重復(fù)問題(比如 id), 會(huì)對(duì)重復(fù)列自動(dòng)添加別名
                .selectCollection(Address.class, UserDTO::getAddressList)
                .leftJoin(Address.class, Address::getUserId, User::getId);
List<UserDTO> dtoList= userMapper.selectJoinList(UserDTO.class, wrapper);

4-5：生成的SQL語句，基于MPJLambdaWrapper代碼，MyBatis-Plus-Join會(huì)生成如下SQL：

SELECT 
    user.id AS user_id,
    user.username AS user_username,
    user.password AS user_password,
    user.age AS user_age,
    user.email AS user_email,
    address.id AS address_id,
    address.user_id AS address_user_id,
    address.province AS address_province,
    address.city AS address_city,
    address.district AS address_district,
    address.detail AS address_detail
FROM 
    user
LEFT JOIN 
    address ON address.user_id = user.id

4-6：執(zhí)行結(jié)果生成sql處理，MyBatis-Plus-Join會(huì)自動(dòng)處理結(jié)果集，將數(shù)據(jù)映射為：

List<UserDTO> dtoList = [
    {
        "id": 1,
        "username": "張三",
        "password": "123456",
        "age": 25,
        "email": "zhangsan@example.com",
        "addressList": [
            {
                "id": 1,
                "userId": 1,
                "province": "北京",
                "city": "北京市",
                "district": "海淀區(qū)",
                "detail": "中關(guān)村大街1號(hào)"
            },
            {
                "id": 2,
                "userId": 1,
                "province": "上海",
                "city": "上海市",
                "district": "浦東新區(qū)",
                "detail": "張江高科技園區(qū)"
            }
        ]
    },
]

注意

//使用如下方法
JoinWrappers.lambda(DoorControllerSettingsDoorInfoDO.class)
//替換
new MPJLambdaWrapper<DoorControllerSettingsDoorInfoDO>()
//使用如下方法
Wrappers.lambda(DoorControllerSettingsDoorInfoDO.class)
//替換
new LambdaWrapper<DoorControllerSettingsDoorInfoDO>()

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