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首页 > 软件编程 > java > Mybatis-plus join连表查询

Mybatis-plus实现join连表查询的示例代码

作者：熟透的蜗牛

mybatis-plus在连表查询上是不行的,如果需要连表查询,就得乖乖的去写xml文件了,本文介绍了mybatis-plus-join框架,它支持连表查询,感兴趣的可以了解一下

最近发现一个好玩的框架，我们知道mybatis-plus在连表查询上是不行的，如果需要连表查询，那么我们就得乖乖的去写xml文件了，但是今天发现一个新的框架 mybatis-plus-join。它既包含了mybatis-plus的所有优点，然后还支持连表查询，还支持对多，对一的查询，行了废话不多说直接看代码吧。

一、数据库DDL

测试的数据库，本测试基于mysql数据库。

/*
 Navicat Premium Data Transfer
 Source Server         : 本地数据库
 Source Server Type    : MySQL
 Source Server Version : 50710
 Source Host           : localhost:3306
 Source Schema         : test-1
 Target Server Type    : MySQL
 Target Server Version : 50710
 File Encoding         : 65001
 Date: 07/12/2022 15:35:14
*/
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for tb_dept
-- ----------------------------
DROP TABLE IF EXISTS `tb_dept`;
CREATE TABLE `tb_dept`  (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `dept_name` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '部门名称',
  `create_time` datetime(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0) ON UPDATE CURRENT_TIMESTAMP(0),
  `update_time` datetime(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0) ON UPDATE CURRENT_TIMESTAMP(0),
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin COMMENT = '部门' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of tb_dept
-- ----------------------------
INSERT INTO `tb_dept` VALUES (1, '人事部', '2022-12-07 13:06:06', '2022-12-07 13:06:06');
INSERT INTO `tb_dept` VALUES (2, '采购部', '2022-12-07 13:06:13', '2022-12-07 13:06:13');
INSERT INTO `tb_dept` VALUES (3, '开发部', '2022-12-07 13:06:17', '2022-12-07 13:06:17');
-- ----------------------------
-- Table structure for tb_post
-- ----------------------------
DROP TABLE IF EXISTS `tb_post`;
CREATE TABLE `tb_post`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `post_name` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '职位名称',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 7 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin COMMENT = '职位' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of tb_post
-- ----------------------------
INSERT INTO `tb_post` VALUES (1, '人事经理');
INSERT INTO `tb_post` VALUES (2, '人事专员');
INSERT INTO `tb_post` VALUES (3, '采购经理');
INSERT INTO `tb_post` VALUES (4, '采购专员');
INSERT INTO `tb_post` VALUES (5, '技术总监');
INSERT INTO `tb_post` VALUES (6, '技术经理');
-- ----------------------------
-- Table structure for tb_user
-- ----------------------------
DROP TABLE IF EXISTS `tb_user`;
CREATE TABLE `tb_user`  (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `user_name` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT NULL COMMENT '用户名',
  `post_id` int(11) NULL DEFAULT NULL COMMENT '职位id',
  `dept_id` int(11) NULL DEFAULT NULL COMMENT '部门id',
  `create_time` datetime(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0) ON UPDATE CURRENT_TIMESTAMP(0) COMMENT '创建时间',
  `update_time` datetime(0) NOT NULL DEFAULT CURRENT_TIMESTAMP(0) ON UPDATE CURRENT_TIMESTAMP(0) COMMENT '修改时间',
  `created` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT 'snail' COMMENT '创建人',
  `updated` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT 'snail' COMMENT '修改人',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 4 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin COMMENT = '测试用户表' ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of tb_user
-- ----------------------------
INSERT INTO `tb_user` VALUES (1, 'admin', 1, 1, '2022-12-07 12:03:20', '2022-12-07 12:03:20', 'snail', 'snail');
INSERT INTO `tb_user` VALUES (2, 'test', 2, 1, '2022-12-07 12:03:51', '2022-12-07 12:03:51', 'snail', 'snail');
INSERT INTO `tb_user` VALUES (3, 'test1', 1, 1, '2022-12-07 12:04:03', '2022-12-07 12:04:03', 'snail', 'snail');
SET FOREIGN_KEY_CHECKS = 1;

二、JAVA代码

实体类

package com.wssnail.model;
import com.baomidou.mybatisplus.annotation.TableName;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import java.time.LocalDateTime;
import java.io.Serializable;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import lombok.EqualsAndHashCode;
/**
 * <p>
 * 测试用户表
 * </p>
 *
 * @author 熟透的蜗牛
 * @since 2022-12-07
 */
@Data
@EqualsAndHashCode(callSuper = false)
@TableName("tb_user")
@ApiModel(value="User对象", description="测试用户表")
public class User implements Serializable {
    private static final long serialVersionUID = 1L;
    @ApiModelProperty(value = "主键")
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    @ApiModelProperty(value = "用户名")
    private String userName;
    @ApiModelProperty(value = "职位id")
    private Integer postId;
    @ApiModelProperty(value = "部门id")
    private Integer deptId;
    @ApiModelProperty(value = "创建时间")
    private LocalDateTime createTime;
    @ApiModelProperty(value = "修改时间")
    private LocalDateTime updateTime;
    @ApiModelProperty(value = "创建人")
    private String created;
    @ApiModelProperty(value = "修改人")
    private String updated;
}
package com.wssnail.model;
import com.baomidou.mybatisplus.annotation.TableName;
import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableId;
import java.io.Serializable;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import lombok.EqualsAndHashCode;
/**
 * <p>
 * 职位
 * </p>
 *
 * @author 熟透的蜗牛
 * @since 2022-12-07
 */
@Data
@EqualsAndHashCode(callSuper = false)
@TableName("tb_post")
@ApiModel(value="Post对象", description="职位")
public class Post implements Serializable {
    private static final long serialVersionUID = 1L;
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    @ApiModelProperty(value = "职位名称")
    private String postName;
}
package com.wssnail.model;
import com.baomidou.mybatisplus.annotation.IdType;
import java.time.LocalDateTime;
import java.io.Serializable;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import lombok.EqualsAndHashCode;
/**
 * <p>
 * 部门
 * </p>
 *
 * @author 熟透的蜗牛
 * @since 2022-12-07
 */
@Data
@EqualsAndHashCode(callSuper = false)
@TableName("tb_dept")
@ApiModel(value="Dept对象", description="部门")
public class Dept implements Serializable {
    private static final long serialVersionUID = 1L;
    @ApiModelProperty(value = "主键")
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    @ApiModelProperty(value = "部门名称")
    private String deptName;
    private LocalDateTime createTime;
    private LocalDateTime updateTime;
}

业务实体类

package com.wssnail.model.bo;
import com.wssnail.model.Post;
import com.wssnail.model.User;
import lombok.Data;
import java.util.List;
/**
 * @Author: 熟透的蜗牛
 * @CreateTime: 2022-12-07 13:57
 * @Description: 一个岗位下有多个人
 * @Version: 1.0
 */
@Data
public class PostUserDo extends Post {
    private List<User> userList;
}
package com.wssnail.model.bo;
import com.wssnail.model.User;
import lombok.Data;
/**
 * @Author: 熟透的蜗牛
 * @CreateTime: 2022-12-07 13:57
 * @Description: TODO
 * @Version: 1.0
 */
@Data
public class UserDo extends User {
    //岗位名称
    private String postName;
    //部门名称
    private String deptName;
}

mapper接口，注意接口不再继承BaseMapper 而是继承了MPJBaseMapper

@Repository
public interface DeptMapper extends MPJBaseMapper<Dept> {
}
@Repository
public interface PostMapper extends MPJBaseMapper<Post> {
}
@Repository
public interface UserMapper extends MPJBaseMapper<User> {
}

service接口也不是继承BaseService而是继承了MPJBaseService，这个继承不是必须的，我这里实现了继承

public interface UserService extends MPJBaseService<User> {
    List<UserDo> listByPage(String postName, String userName);
}
public interface PostService extends MPJBaseService<Post> {
    List <PostUserDo> listPostUser();
}
public interface DeptService extends MPJBaseService<Dept> {
}

service接口实现类，代码里有详细注释

简单的连表查询

package com.wssnail.service.impl;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.github.yulichang.base.MPJBaseServiceImpl;
import com.github.yulichang.wrapper.MPJLambdaWrapper;
import com.wssnail.mapper.UserMapper;
import com.wssnail.model.Dept;
import com.wssnail.model.Post;
import com.wssnail.model.User;
import com.wssnail.model.bo.UserDo;
import com.wssnail.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
/**
 * <p>
 * 测试用户表 服务实现类
 * </p>
 *
 * @author 熟透的蜗牛
 * @since 2022-12-07
 */
@Service
public class UserServiceImpl extends MPJBaseServiceImpl<UserMapper, User> implements UserService {
    @Autowired
    private UserMapper userMapper; //这里对应主表的mapper
    /*
     * @description:
     * 连表分页查询,以下示例代码为左连接查询
     * 内连接方法 innerJoin()
     * 右连接方法 rightJoin() 和这个使用方法一样
     * @date: 2022/12/7 14:05
     * @param postName
     * @param userName
     * @return: java.util.List<com.wssnail.model.bo.UserDo>
     **/
    @Override
    public List<UserDo> listByPage(String postName, String userName) {
        MPJLambdaWrapper<User> userMPJLambdaWrapper = new MPJLambdaWrapper<User>()
                .selectAll(User.class) //查询主表所有的字段
                .select(Dept::getDeptName) //查询部门表的部门名称
                .select(Post::getPostName) //查询岗位表的 岗位名称
                .leftJoin(Dept.class, Dept::getId, User::getDeptId) //左连接查询，相当于 left join dept on dept.id=user.dept_id
                .leftJoin(Post.class, Post::getId, User::getPostId) // 左连接查询，相当于 left join post on post.id=user.post_id
                .eq(Post::getPostName, postName)
                .like(User::getUserName, userName);
        //返回自定义的数据，相当于执行如下SQL，可以看出主表别名为t 其他表名依次为t1,t2.........
        //        SELECT
        //        t.id,
        //        t.user_name,
        //        t.post_id,
        //        t.dept_id,
        //        t.create_time,
        //        t.update_time,
        //        t.created,
        //        t.updated,
        //        t1.dept_name,
        //        t2.post_name
        //        FROM
        //        tb_user t
        //        LEFT JOIN tb_dept t1 ON ( t1.id = t.dept_id )
        //        LEFT JOIN tb_post t2 ON ( t2.id = t.post_id )
        //        WHERE
        //                (
        //                        t2.post_name = ?
        //                AND t.user_name LIKE ?)
//        List<UserDo> userDos = userMapper.selectJoinList(UserDo.class, userMPJLambdaWrapper);
//        return userDos;
        //分页查询等于执行如下SQL，分页查询需要 配置mybatis plus 分页插件，详情见 com.wssnail.config.MybatisPageConfig 类
//        SELECT
//        t.id,
//        t.user_name,
//        t.post_id,
//        t.dept_id,
//        t.create_time,
//        t.update_time,
//        t.created,
//        t.updated,
//        t1.dept_name,
//        t2.post_name
//        FROM
//        tb_user t
//        LEFT JOIN tb_dept t1 ON ( t1.id = t.dept_id )
//        LEFT JOIN tb_post t2 ON ( t2.id = t.post_id )
//        WHERE
//                (
//                        t2.post_name = ?
//                AND t.user_name LIKE ?)
//        LIMIT ?
        Page<User> page = new Page<>();
        IPage<UserDo> userDoIPage = userMapper.selectJoinPage(page, UserDo.class, userMPJLambdaWrapper);
        return userDoIPage.getRecords();
    }
}

对多查询

package com.wssnail.service.impl;
import com.github.yulichang.base.MPJBaseServiceImpl;
import com.github.yulichang.wrapper.MPJLambdaWrapper;
import com.wssnail.mapper.PostMapper;
import com.wssnail.model.Post;
import com.wssnail.model.User;
import com.wssnail.model.bo.PostUserDo;
import com.wssnail.service.PostService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import java.util.List;
/**
 * <p>
 * 职位 服务实现类
 * </p>
 *
 * @author 熟透的蜗牛
 * @since 2022-12-07
 */
@Service
public class PostServiceImpl extends MPJBaseServiceImpl<PostMapper, Post> implements PostService {
    @Autowired
    private PostMapper postMapper;
    @Override
    public List<PostUserDo> listPostUser() {
        //相当于执行如下SQL ，以下示例代码是对多查询，对一查询使用 selectAssociation()方法，用法与此相同
//        SELECT
//        t.id,
//        t.post_name,
//        t1.id AS join_id,
//        t1.user_name,
//        t1.post_id,
//        t1.dept_id,
//        t1.create_time,
//        t1.update_time,
//        t1.created,
//        t1.updated
//        FROM
//        tb_post t
//        LEFT JOIN tb_user t1 ON (
//                t1.post_id = t.id)
//        等价于 如下的xml配置
//        <resultMap id="xxxxxxxx" type="com.wssnail.model.bo.PostUserDo">
//            <result property="id" column="id"/>
//            <result property="postName" column="post_name"/>
//            <!--其他属性省略-->
//            <collection property="userList" javaType="java.util.List"
//                ofType="com.wssnail.model.User">
//                <id property="id" column="id"/>
//                <result property="userName" column="user_name"/>
//                <!--其他属性省略-->
//            </collection>
//        </resultMap>
        //返回数据如下 ，注意由于嵌套结果方式会导致结果集被折叠，因此分页查询的结果在折叠后总数会减少，所以无法保证分页结果数量正确。
//       [{
//            "id": 1,
//            "postName": "人事经理",
//            "userList": [{
//                "id": 1,
//                "userName": "admin",
//                "postId": 1,
//                "deptId": 1,
//                "createTime": "2022-12-07T12:03:20",
//                "updateTime": "2022-12-07T12:03:20",
//                "created": "snail",
//                "updated": "snail"
//            }, {
//                "id": 3,
//                "userName": "test1",
//                "postId": 1,
//                "deptId": 1,
//                "createTime": "2022-12-07T12:04:03",
//                "updateTime": "2022-12-07T12:04:03",
//                "created": "snail",
//                "updated": "snail"
//            }]
//        }, {
//            "id": 2,
//            "postName": "人事专员",
//            "userList": [{
//                "id": 2,
//                "userName": "test",
//                "postId": 2,
//                "deptId": 1,
//                "createTime": "2022-12-07T12:03:51",
//                "updateTime": "2022-12-07T12:03:51",
//                "created": "snail",
//                "updated": "snail"
//            }]
//        }, {
//            "id": 3,
//            "postName": "采购经理",
//            "userList": []
//        }]
        MPJLambdaWrapper<Post> postMPJLambdaWrapper = new MPJLambdaWrapper<Post>().selectAll(Post.class)
                .selectCollection(User.class, PostUserDo::getUserList)
                .leftJoin(User.class, User::getPostId, Post::getId);//一对多查询
        List<PostUserDo> postUserDos = postMapper.selectJoinList(PostUserDo.class, postMPJLambdaWrapper);
        return postUserDos;
    }
}

分页配置 

package com.wssnail.config;
import com.baomidou.mybatisplus.annotation.DbType;
import com.baomidou.mybatisplus.extension.plugins.MybatisPlusInterceptor;
import com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class MybatisPageConfig {
    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
        interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));
        return interceptor;
    }
}

三、pom依赖和配置文件

server:
  port: 8090
spring:
  application:
    name: test
  datasource:
    url: jdbc:mysql://127.0.0.1:3306/test-1?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=convertToNull&useSSL=false&allowMultiQueries=true&serverTimezone=Asia/Shanghai
    username: root
    password: snail
pagehelper:
  helper-dialect: mysql
  reasonable: true
  support-methods-arguments: false
  params: count=countsql
  #打印sql
mybatis-plus:
  configuration:
    mapper-locations: classpath*:mapper/*Mapper.xml
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.wssnail</groupId>
    <artifactId>test-mybatis-plus-join</artifactId>
    <version>1.0-SNAPSHOT</version>
    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.2</version>
        <relativePath/>
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.12.0</version>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.2</version>
        </dependency>
        <dependency>
            <groupId>com.github.yulichang</groupId>
            <artifactId>mybatis-plus-join-boot-starter</artifactId>
            <version>1.3.8</version>
        </dependency>
        <!--swagger-->
        <dependency>
            <groupId>com.spring4all</groupId>
            <artifactId>swagger-spring-boot-starter</artifactId>
            <version>1.9.1.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>com.github.xiaoymin</groupId>
            <artifactId>swagger-bootstrap-ui</artifactId>
            <version>1.9.6</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.24</version>
        </dependency>
    </dependencies>
</project>

以上就是本人测试的结果，还有很多使用方法没有一一验证，如果感兴趣的可以参考源代码，自己动手试试

https://gitee.com/best_handsome/mybatis-plus-join 

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