整合SpringBoot Mybatis-Puls-join 多表联查及分页（保姆级详细教程）

前言

• MyBatis-Plus-Join （简称 MPJ）是一个 MyBatis-Plus的增强工具，在 MyBatis-Plus 的基础上只做增强不做改变，为简化开发、提高效率而生。
• 无侵入：只做增强不做改变，引入它不会对现有工程产生影响，如丝般顺滑
• 无感引入, 支持MP风格的查询, 您会MP就会MPJ, 无需额外的学习成本
• 兼容MP的别名、逻辑删除、枚举列、TypeHandle列等特性
• 支持注解形式一对一、一对多和连表查询形式的一对一和一对多

官网：mybatis-plus-join官网

一、新建SpringBoot项目

1.1、自选依赖

二、 mybatis-plus-join

2.1、导入依赖

  <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-bootstrap</artifactId>
            <version>3.1.7</version>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.5</version>
        </dependency>
        <dependency>
            <groupId>com.github.yulichang</groupId>
            <artifactId>mybatis-plus-join-boot-starter</artifactId>
            <version>1.4.11</version>
        </dependency>

2.2、修改配置文件

mybatis-plus-join配置文件如下：

# mybatis-plus配置
mybatis-plus:
  # 启动检查MyBatis配置文件
  check-config-location: false
  # MyBatis配置文件位置
  config-location:
  # MyBaits别名包扫描路径
  type-aliases-package: com.ui.springbootmybatisplusjoin.mybatis.entity
  # Mapper所对应的XML文件位置 默认【classpath*:/mapper/**/*.xml】
  mapper-locations: classpath:mappers/*xml
  # TypeHandler扫描路径
  type-handlers-package:
  configuration:
    # 日志打印
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    # 是否开启自动驼峰命名规则
    map-underscore-to-camel-case: true
    # 开启Mybatis二级缓存，默认为true
    cache-enabled: true
  global-config:
    # 控制台mybatis-plus的logo
    banner: true
    db-config:
      # 全局默认主键类型
      id-type: auto
      # 逻辑删除配置
      logic-delete-field: deleted
      logic-delete-value: 1
      logic-not-delete-value: 0

2.3、实体类

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.beans.factory.annotation.Autowired;

/**
 * @ClassName User
 * @Description 描述
 * @Author 轸...
 * @Date 2024/9/28 20:15
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("user")
public class User {

    @TableId(value = "user_id",type = IdType.AUTO)
    private Long userId;

    @TableField("user_name")
    private String userName;

    @TableField("user_account")
    private String userAccount;

    @TableField("user_pwd")
    private String userPwd;

    @TableField("user_tel")
    private String userTel;

    @TableField("clazz_id")
    private Integer clazzId;

    @TableField(exist = false)
    private String clazzName;
}

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

/**
 * @ClassName Log
 * @Description 描述
 * @Author 轸...
 * @Date 2024/9/28 20:15
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("clazz")
public class Clazz {

    @TableId(value = "clazz_id",type = IdType.AUTO)
    private Long clazzId;

    @TableField("clazz_name")
    private String clazzName;

}

2.4、mapper 配置 mapper 扫描路径

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.ui.springbootmybatisplusjoin.demos.mapper")
public class SpringBootMybatisPlusJoinApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootMybatisPlusJoinApplication.class, args);
    }

}

2.5、service 以及 serviceImpl

三、mybatis-plus-join 分页联查

3.1、增加Vo实体类 分页参数

3.2、分页列表及联查业务层

import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.github.yulichang.base.MPJBaseServiceImpl;
import com.github.yulichang.wrapper.MPJLambdaWrapper;
import com.ui.springbootmybatisplusjoin.demos.mapper.UserMapper;
import com.ui.springbootmybatisplusjoin.demos.pojo.Clazz;
import com.ui.springbootmybatisplusjoin.demos.pojo.User;
import com.ui.springbootmybatisplusjoin.demos.pojo.Vo.UserVo;
import com.ui.springbootmybatisplusjoin.demos.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * @ClassName UserServiceImpl
 * @Description 描述
 * @Author 轸...
 * @Date 2024/9/28 20:22
 */
@Service
public class UserServiceImpl extends MPJBaseServiceImpl<UserMapper, User> implements UserService {

    @Autowired
    private UserMapper userMapper;
    /**
     * mybatis-plus-join 联查及分页
     * @param userVo
     * @return
     */
    @Override
    public Page<User> pageList(UserVo userVo) {

        // SELECT t.*,t1.clazz_name FROM user t LEFT JOIN clazz t1 ON t.clazz_id = t1.clazz_id  LIMIT ?,?
        MPJLambdaWrapper<User> lambdaWrapper = new MPJLambdaWrapper<>();
        lambdaWrapper.selectAll(User.class)
                .select(Clazz::getClazzName)
                .leftJoin(Clazz.class,Clazz::getClazzId,User::getClazzId);
        Page<User> userPage = new Page<>(userVo.getPageNum(), userVo.getPageSize());

        return userMapper.selectJoinPage(userPage, User.class,lambdaWrapper);
    }
}

3.3、控制层

四、以上步骤 启动执行方法时会报一个com.baomidou.mybatisplus.core.exceptions.MybatisPlusException: mapper not find by class <Clazz> , add mapper and extends BaseMapper<T> or MPJBaseMapper<T>这样的错误

这个错误是因为 找不到联查表的mapper

所以我们应该写一个 clazzMapper

import com.github.yulichang.base.MPJBaseMapper;
import com.ui.springbootmybatisplusjoin.demos.pojo.Clazz;

/**
 * @ClassName ClazzMapper
 * @Description 描述
 * @Author 轸...
 * @Date 2024/9/28 20:53
 */

public interface ClazzMapper extends MPJBaseMapper<Clazz> {
}

六、测试