Springboot整合mybatis+mybatis-plus+PageHelper

公良同
2023-12-01

Mybatis是在国内使用是最广泛的,以前都是使用xml进行映射,说实话真心不太好用,维护起来也不太方便。 从mybatis3.0后开始支持 @Mapper注解,极大方便了开发,几乎不在需要任何xml进行配置了。下面重点就讲下Mybatis的相关整合与@Mapper的使用。

首先,配置pom.xml文件,添加以下配置项

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.4</version>
</dependency>
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.1</version>
</dependency>

第二步,在application.yml配置文件中添加以下配置项

spring:
  datasource:
    platform: mysql
    url: jdbc:mysql://localhost/jeealfa_boot?useUnicode=true&characterEncoding=utf-8&zeroDateTimeBehavior=convertToNull&transformedBitIsBoolean=true&autoReconnect=true&failOverReadOnly=false
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
    initialization-mode: never
    schema: classpath:db/schema.sql
# 配置slq打印日志
mybatis-plus:
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    map-underscore-to-camel-case: true

schema.sql文件内容户名测试要用,可以收到创建数据库,然后运行,如下: 也可以把 initialization-mode值设为always, 首次运行后修改为never.

drop table IF exists `user`;
create table `user`(
  `id` int(11) not null auto_increment,
  `name` varchar(60) not null default "" comment "姓名",
  `age` int(11) not null default 0,
  primary key (`id`),
  unique key (`name`)
)engine=InnoDB default charset=utf8;

第三步,创建数据model,内容如下

package com.jeealfa.model;

import lombok.Data;

@Data
public class User {
    private int id;
    private String name;
    private int age;
}

第四步,创建UserMapper,内容如下

package com.jeealfa.mapper;

import com.jeealfa.model.User;
import org.apache.ibatis.annotations.*;

@Mapper
public interface UserMapper {
    @Select("SELECT * FROM user WHERE id = #{id}")
    User queryById(@Param("id") int id);

    @Insert("INSERT INTO user(name,age) VALUES(#{name},#{age})")
    int add(User user);

    @Delete("DELETE FROM user WHERE id = #{id}")
    int delById(int id);

    @Update("UPDATE user SET name=#{name},age=#{age} WHERE id=#{id}")
    int updateById(User user);
}

第五步,在Controller中使用

//省略
@RestController
@RequestMapping("/user")
public class UserController {
    @Autowired
    private UserMapper userMapper;

    @RequestMapping("/querybyid")
    public User queryById(int id){
        return userMapper.queryById(id);
    }

    @RequestMapping("/add")
    public String add(User user){
        return userMapper.add(user) == 1?"success":"failed";
    }
}

第六步,mybatis-plus提供了BaseMapper,提供了一些列通用功能,极大方便了Mapper的开发,使用中可以直接继承此接口。BaseMapper提供的功能有:

package com.baomidou.mybatisplus.core.mapper;

import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import java.io.Serializable;
import java.util.Collection;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.annotations.Param;

public interface BaseMapper<T> extends Mapper<T> {
    int insert(T entity);

    int deleteById(Serializable id);

    int deleteByMap(@Param("cm") Map<String, Object> columnMap);

    int delete(@Param("ew") Wrapper<T> queryWrapper);

    int deleteBatchIds(@Param("coll") Collection<? extends Serializable> idList);

    int updateById(@Param("et") T entity);

    int update(@Param("et") T entity, @Param("ew") Wrapper<T> updateWrapper);

    T selectById(Serializable id);

    List<T> selectBatchIds(@Param("coll") Collection<? extends Serializable> idList);

    List<T> selectByMap(@Param("cm") Map<String, Object> columnMap);

    T selectOne(@Param("ew") Wrapper<T> queryWrapper);

    Integer selectCount(@Param("ew") Wrapper<T> queryWrapper);

    List<T> selectList(@Param("ew") Wrapper<T> queryWrapper);

    List<Map<String, Object>> selectMaps(@Param("ew") Wrapper<T> queryWrapper);

    List<Object> selectObjs(@Param("ew") Wrapper<T> queryWrapper);

    <E extends IPage<T>> E selectPage(E page, @Param("ew") Wrapper<T> queryWrapper);

    <E extends IPage<Map<String, Object>>> E selectMapsPage(E page, @Param("ew") Wrapper<T> queryWrapper);
}

UserMapper可以改为

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

第7步,整合pageHelper, 在pom.xml里添加

<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-starter</artifactId>
    <version>1.2.3</version>
</dependency>
<dependency>
    <groupId>com.github.pagehelper</groupId>
    <artifactId>pagehelper-spring-boot-autoconfigure</artifactId>
    <version>1.2.3</version>
</dependency>

在application.yml里新增如下篇日志项:

pagehelper:
  helper-dialect: mysql
  reasonable: true
  support-methods-arguments: true
  params: count=countSql

第8步,在控制器中使用分页

@RequestMapping("/user/list")
public Page<User> getMap(@RequestParam(value = "page", defaultValue = "0") int page,
                         @RequestParam(value = "size", defaultValue = "5") int size){
    PageHelper.startPage(page, size, "id desc");
    Page<User> list = userMapper.listAll();
    System.out.println(list);
    return list;
}

注意:PageHelper.startPage执行之后,必须紧跟列表查询方法,不然分页可能会不起作用。

UserMapper中添加listAll接口方法,如下

package com.jeealfa.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.github.pagehelper.Page;
import com.jeealfa.model.User;
import org.apache.ibatis.annotations.*;

@Mapper
public interface UserMapper2 extends BaseMapper<User> {

    @Select("SELECT * FROM user")
    Page<User> listAll();

}

可通过postman进行测试。

第9步,自定义sql。 Mybatis提供了@SelectProvider注解来进行自定义sql查询。

见下面事例:

package com.jeealfa.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.github.pagehelper.Page;
import com.jeealfa.model.User;
import org.apache.ibatis.annotations.*;
import org.apache.ibatis.builder.annotation.ProviderContext;
import org.apache.ibatis.jdbc.SQL;

import java.util.List;
import java.util.Map;

@Mapper
public interface UserMapper extends BaseMapper<User> {

    @Select("SELECT * FROM user")
    Page<User> listAll();

    @SelectProvider(type = UserMapper.SelectSql.class, method = "sql")
    List<User> queryByPage(Page page, @Param("orderby") String orderby);
    
    class SelectSql{
        public String sql(Object object, ProviderContext context){
            Map map = (Map) object;
            Page page = (Page) map.get("page");
            String orderby = (String) map.get("orderby");

            return (new SQL()).SELECT("*").FROM("user").
                    ORDER_BY(orderby).
                    LIMIT(page.getStartRow()+","+page.getPageSize())
                    .toString();
        }
    }
}

自定义sql是灵活的,利用SelectProvider, 甚至可以自己手动写一个BaseMapper。

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