mybatis-plus教程-Mybatis-Plus增删改查

2023-11-04

完整代码

https://github.com/pbteach/mybatis-plus-test

Mybatis-plus增删改查

通过前面的学习，我们了解到通过继承BaseMapper就可以获取到各种各样的单表操作，接下来我们将详细讲解这些操作。

1556351189202

插入操作

方法定义

    /**
     * 插入一条记录
     *
     * @param entity 实体对象
     */
    int insert(T entity);

测试用例

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testInsert(){
        User user = new User();
        user.setAge(20);
        user.setEmail("test@pbteach.com");
        user.setName("曹操");
        user.setUserName("caocao");
        user.setPassword("123456");

        int result = this.userMapper.insert(user); //返回的result是受影响的行数，并不是自增后的id
        System.out.println("result = " + result); 

        System.out.println(user.getId()); //自增后的id会回填到对象中
    }

}

测试

[main] [com.pbteach.mp.mapper.UserMapper.insert]-[DEBUG] ==>  Preparing: INSERT INTO tb_user ( id, user_name, password, name, age, email ) VALUES ( ?, ?, ?, ?, ?, ? ) 
[main] [com.pbteach.mp.mapper.UserMapper.insert]-[DEBUG] ==> Parameters: 1122045867793072130(Long), caocao(String), 123456(String), 曹操(String), 20(Integer), test@pbteach.com(String)
[main] [com.pbteach.mp.mapper.UserMapper.insert]-[DEBUG] <==    Updates: 1
[main] [org.mybatis.spring.SqlSessionUtils]-[DEBUG] Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@411291e5]
result = 1
1122045867793072130

1573691210439

可以看到，数据已经写入到了数据库，但是，id的值不正确，我们期望的是数据库自增长，实际是MP生成了id的值写入到了数据库。

如何设置id的生成策略呢？

MP支持的id策略：

package com.baomidou.mybatisplus.annotation;

import lombok.Getter;

/**
 * 生成ID类型枚举类
 *
 * @author hubin
 * @since 2015-11-10
 */
@Getter
public enum IdType {
    /**
     * 数据库ID自增
     */
    AUTO(0),
    /**
     * 该类型为未设置主键类型
     */
    NONE(1),
    /**
     * 用户输入ID
     * <p>该类型可以通过自己注册自动填充插件进行填充</p>
     */
    INPUT(2),

    /* 以下3种类型、只有当插入对象ID 为空，才自动填充。 */
    /**
     * 全局唯一ID (idWorker)
     */
    ID_WORKER(3),
    /**
     * 全局唯一ID (UUID)
     */
    UUID(4),
    /**
     * 字符串全局唯一ID (idWorker 的字符串表示)
     */
    ID_WORKER_STR(5);

    private final int key;

    IdType(int key) {
        this.key = key;
    }
}

修改User对象：

package com.pbteach.mp.pojo;

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

@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("tb_user")
public class User {

    @TableId(type = IdType.AUTO) //指定id类型为自增长
    private Long id;
    private String userName;
    private String password;
    private String name;
    private Integer age;
    private String email;
}

数据插入成功：

1573691233384

@TableField

在MP中通过@TableField注解可以指定字段的一些属性，常常解决的问题有2个：

1、对象中的属性名和字段名不一致的问题（非驼峰）

2、对象中的属性字段在表中不存在的问题

使用：

1556362315190

其他用法，如大字段不加入查询字段：

1556362597538

效果：

1556362621608

更新操作

在MP中，更新操作有2种，一种是根据id更新，另一种是根据条件更新。

根据id更新

方法定义：

    /**
     * 根据 ID 修改
     *
     * @param entity 实体对象
     */
    int updateById(@Param(Constants.ENTITY) T entity);

测试：

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testUpdateById() {
        User user = new User();
        user.setId(6L); //主键
        user.setAge(21); //更新的字段

        //根据id更新，更新不为null的字段
        this.userMapper.updateById(user);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.updateById]-[DEBUG] ==>  Preparing: UPDATE tb_user SET age=? WHERE id=? 
[main] [com.pbteach.mp.mapper.UserMapper.updateById]-[DEBUG] ==> Parameters: 21(Integer), 6(Long)
[main] [com.pbteach.mp.mapper.UserMapper.updateById]-[DEBUG] <==    Updates: 1

1573691255238

根据条件更新

方法定义：

    /**
     * 根据 whereEntity 条件，更新记录
     *
     * @param entity        实体对象 (set 条件值,可以为 null)
     * @param updateWrapper 实体对象封装操作类（可以为 null,里面的 entity 用于生成 where 语句）
     */
    int update(@Param(Constants.ENTITY) T entity, @Param(Constants.WRAPPER) Wrapper<T> updateWrapper);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import com.baomidou.mybatisplus.core.conditions.Wrapper;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.conditions.update.UpdateWrapper;
import net.minidev.json.writer.UpdaterMapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testUpdate() {
        User user = new User();
        user.setAge(22); //更新的字段

        //更新的条件
        QueryWrapper<User> wrapper = new QueryWrapper<>();
        wrapper.eq("id", 6);

        //执行更新操作
        int result = this.userMapper.update(user, wrapper);
        System.out.println("result = " + result);
    }

}

或者，通过UpdateWrapper进行更新：

    @Test
    public void testUpdate() {
        //更新的条件以及字段
        UpdateWrapper<User> wrapper = new UpdateWrapper<>();
        wrapper.eq("id", 6).set("age", 23);

        //执行更新操作
        int result = this.userMapper.update(null, wrapper);
        System.out.println("result = " + result);
    }

测试结果：

[main] [com.pbteach.mp.mapper.UserMapper.update]-[DEBUG] ==>  Preparing: UPDATE tb_user SET age=? WHERE id = ? 
[main] [com.pbteach.mp.mapper.UserMapper.update]-[DEBUG] ==> Parameters: 23(Integer), 6(Integer)
[main] [com.pbteach.mp.mapper.UserMapper.update]-[DEBUG] <==    Updates: 1

均可达到更新的效果。

关于wrapper更多的用法后面会详细讲解。

删除操作

deleteById

方法定义：

/**
 * 根据 ID 删除
 *
 * @param id 主键ID
 */
int deleteById(Serializable id);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testDeleteById() {
        //执行删除操作
        int result = this.userMapper.deleteById(6L);
        System.out.println("result = " + result);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.deleteById]-[DEBUG] ==>  Preparing: DELETE FROM tb_user WHERE id=? 
[main] [com.pbteach.mp.mapper.UserMapper.deleteById]-[DEBUG] ==> Parameters: 6(Long)
[main] [com.pbteach.mp.mapper.UserMapper.deleteById]-[DEBUG] <==    Updates: 1

1573691274395

数据被删除。

deleteByMap

方法定义：

    /**
     * 根据 columnMap 条件，删除记录
     *
     * @param columnMap 表字段 map 对象
     */
    int deleteByMap(@Param(Constants.COLUMN_MAP) Map<String, Object> columnMap);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.HashMap;
import java.util.Map;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testDeleteByMap() {
        Map<String, Object> columnMap = new HashMap<>();
        columnMap.put("age",20);
        columnMap.put("name","张三");

        //将columnMap中的元素设置为删除的条件，多个之间为and关系
        int result = this.userMapper.deleteByMap(columnMap);
        System.out.println("result = " + result);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.deleteByMap]-[DEBUG] ==>  Preparing: DELETE FROM tb_user WHERE name = ? AND age = ? 
[main] [com.pbteach.mp.mapper.UserMapper.deleteByMap]-[DEBUG] ==> Parameters: 张三(String), 20(Integer)
[main] [com.pbteach.mp.mapper.UserMapper.deleteByMap]-[DEBUG] <==    Updates: 0

delete

方法定义：

/**
 * 根据 entity 条件，删除记录
 *
 * @param wrapper 实体对象封装操作类（可以为 null）
 */
int delete(@Param(Constants.WRAPPER) Wrapper<T> wrapper);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.HashMap;
import java.util.Map;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testDeleteByMap() {
        User user = new User();
        user.setAge(20);
        user.setName("张三");

        //将实体对象进行包装，包装为操作条件
        QueryWrapper<User> wrapper = new QueryWrapper<>(user);

        int result = this.userMapper.delete(wrapper);
        System.out.println("result = " + result);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.delete]-[DEBUG] ==>  Preparing: DELETE FROM tb_user WHERE name=? AND age=? 
[main] [com.pbteach.mp.mapper.UserMapper.delete]-[DEBUG] ==> Parameters: 张三(String), 20(Integer)
[main] [com.pbteach.mp.mapper.UserMapper.delete]-[DEBUG] <==    Updates: 0

deleteBatchIds

方法定义：

    /**
     * 删除（根据ID 批量删除）
     *
     * @param idList 主键ID列表(不能为 null 以及 empty)
     */
    int deleteBatchIds(@Param(Constants.COLLECTION) Collection<? extends Serializable> idList);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testDeleteByMap() {
        //根据id集合批量删除
        int result = this.userMapper.deleteBatchIds(Arrays.asList(1L,10L,20L));
        System.out.println("result = " + result);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.deleteBatchIds]-[DEBUG] ==>  Preparing: DELETE FROM tb_user WHERE id IN ( ? , ? , ? ) 
[main] [com.pbteach.mp.mapper.UserMapper.deleteBatchIds]-[DEBUG] ==> Parameters: 1(Long), 10(Long), 20(Long)
[main] [com.pbteach.mp.mapper.UserMapper.deleteBatchIds]-[DEBUG] <==    Updates: 1

查询操作

MP提供了多种查询操作，包括根据id查询、批量查询、查询单条数据、查询列表、分页查询等操作。

selectById

方法定义：

    /**
     * 根据 ID 查询
     *
     * @param id 主键ID
     */
    T selectById(Serializable id);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectById() {
        //根据id查询数据
        User user = this.userMapper.selectById(2L);
        System.out.println("result = " + user);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.selectById]-[DEBUG] ==>  Preparing: SELECT id,user_name,password,name,age,email FROM tb_user WHERE id=? 
[main] [com.pbteach.mp.mapper.UserMapper.selectById]-[DEBUG] ==> Parameters: 2(Long)
[main] [com.pbteach.mp.mapper.UserMapper.selectById]-[DEBUG] <==      Total: 1

result = User(id=2, userName=lisi, password=123456, name=李四, age=20, email=test2@pbteach.com, address=null)

selectBatchIds

方法定义：

/**
 * 查询（根据ID 批量查询）
 *
 * @param idList 主键ID列表(不能为 null 以及 empty)
 */
List<T> selectBatchIds(@Param(Constants.COLLECTION) Collection<? extends Serializable> idList);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.Arrays;
import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectBatchIds() {
        //根据id集合批量查询
        List<User> users = this.userMapper.selectBatchIds(Arrays.asList(2L, 3L, 10L));
        for (User user : users) {
            System.out.println(user);
        }
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.selectBatchIds]-[DEBUG] ==>  Preparing: SELECT id,user_name,password,name,age,email FROM tb_user WHERE id IN ( ? , ? , ? ) 
[main] [com.pbteach.mp.mapper.UserMapper.selectBatchIds]-[DEBUG] ==> Parameters: 2(Long), 3(Long), 10(Long)
[main] [com.pbteach.mp.mapper.UserMapper.selectBatchIds]-[DEBUG] <==      Total: 2

User(id=2, userName=lisi, password=123456, name=李四, age=20, email=test2@pbteach.com, address=null)
User(id=3, userName=wangwu, password=123456, name=王五, age=28, email=test3@pbteach.com, address=null)

selectOne

方法定义：

/**
 * 根据 entity 条件，查询一条记录
 *
 * @param queryWrapper 实体对象封装操作类（可以为 null）
 */
T selectOne(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectOne() {
        QueryWrapper<User> wrapper = new QueryWrapper<User>();
        wrapper.eq("name", "李四");

        //根据条件查询一条数据，如果结果超过一条会报错
        User user = this.userMapper.selectOne(wrapper);
        System.out.println(user);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.selectOne]-[DEBUG] ==>  Preparing: SELECT id,user_name,password,name,age,email FROM tb_user WHERE name = ? 
[main] [com.pbteach.mp.mapper.UserMapper.selectOne]-[DEBUG] ==> Parameters: 李四(String)
[main] [com.pbteach.mp.mapper.UserMapper.selectOne]-[DEBUG] <==      Total: 1

User(id=2, userName=lisi, password=123456, name=李四, age=20, email=test2@pbteach.com, address=null)

selectCount

方法定义：

/**
 * 根据 Wrapper 条件，查询总记录数
 *
 * @param queryWrapper 实体对象封装操作类（可以为 null）
 */
Integer selectCount(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectCount() {
        QueryWrapper<User> wrapper = new QueryWrapper<User>();
        wrapper.gt("age", 23); //年龄大于23岁

        //根据条件查询数据条数
        Integer count = this.userMapper.selectCount(wrapper);
        System.out.println("count = " + count);
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.selectCount]-[DEBUG] ==>  Preparing: SELECT COUNT( 1 ) FROM tb_user WHERE age > ? 
[main] [com.pbteach.mp.mapper.UserMapper.selectCount]-[DEBUG] ==> Parameters: 23(Integer)
[main] [com.pbteach.mp.mapper.UserMapper.selectCount]-[DEBUG] <==      Total: 1

count = 2

selectList

方法定义：

/**
 * 根据 entity 条件，查询全部记录
 *
 * @param queryWrapper 实体对象封装操作类（可以为 null）
 */
List<T> selectList(@Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectList() {
        QueryWrapper<User> wrapper = new QueryWrapper<User>();
        wrapper.gt("age", 23); //年龄大于23岁

        //根据条件查询数据
        List<User> users = this.userMapper.selectList(wrapper);
        for (User user : users) {
            System.out.println("user = " + user);
        }
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.selectList]-[DEBUG] ==>  Preparing: SELECT id,user_name,password,name,age,email FROM tb_user WHERE age > ? 
[main] [com.pbteach.mp.mapper.UserMapper.selectList]-[DEBUG] ==> Parameters: 23(Integer)
[main] [com.pbteach.mp.mapper.UserMapper.selectList]-[DEBUG] <==      Total: 2

user = User(id=3, userName=wangwu, password=123456, name=王五, age=28, email=test3@pbteach.com, address=null)
user = User(id=5, userName=sunqi, password=123456, name=孙七, age=24, email=test5@pbteach.com, address=null)

selectPage

方法定义：

/**
 * 根据 entity 条件，查询全部记录（并翻页）
 *
 * @param page         分页查询条件（可以为 RowBounds.DEFAULT）
 * @param queryWrapper 实体对象封装操作类（可以为 null）
 */
IPage<T> selectPage(IPage<T> page, @Param(Constants.WRAPPER) Wrapper<T> queryWrapper);

配置分页插件：

package com.pbteach.mp;

import com.baomidou.mybatisplus.extension.plugins.PaginationInterceptor;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
@MapperScan("com.pbteach.mp.mapper") //设置mapper接口的扫描包
public class MybatisPlusConfig {

    /**
     * 分页插件
     */
    @Bean
    public PaginationInterceptor paginationInterceptor() {
        return new PaginationInterceptor();
    }
}

测试用例：

package com.pbteach.mp;

import com.pbteach.mp.mapper.UserMapper;
import com.pbteach.mp.pojo.User;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class UserMapperTest {

    @Autowired
    private UserMapper userMapper;

    @Test
    public void testSelectPage() {
        QueryWrapper<User> wrapper = new QueryWrapper<User>();
        wrapper.gt("age", 20); //年龄大于20岁

        Page<User> page = new Page<>(1,1);

        //根据条件查询数据
        IPage<User> iPage = this.userMapper.selectPage(page, wrapper);
        System.out.println("数据总条数：" + iPage.getTotal());
        System.out.println("总页数：" + iPage.getPages());


        List<User> users = iPage.getRecords();
        for (User user : users) {
            System.out.println("user = " + user);
        }
    }

}

结果：

[main] [com.pbteach.mp.mapper.UserMapper.selectPage]-[DEBUG] ==>  Preparing: SELECT COUNT(1) FROM tb_user WHERE age > ? 
[main] [com.pbteach.mp.mapper.UserMapper.selectPage]-[DEBUG] ==> Parameters: 20(Integer)
[main] [com.pbteach.mp.mapper.UserMapper.selectPage]-[DEBUG] ==>  Preparing: SELECT id,user_name,password,name,age,email FROM tb_user WHERE age > ? LIMIT ?,? 
[main] [com.pbteach.mp.mapper.UserMapper.selectPage]-[DEBUG] ==> Parameters: 20(Integer), 0(Long), 1(Long)
[main] [com.pbteach.mp.mapper.UserMapper.selectPage]-[DEBUG] <==      Total: 1
[main] [org.mybatis.spring.SqlSessionUtils]-[DEBUG] Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6ecd665]
数据总条数：3
总页数：3
user = User(id=3, userName=wangwu, password=123456, name=王五, age=28, email=test3@pbteach.com, address=null)

SQL注入的原理

前面我们已经知道，MP在启动后会将BaseMapper中的一系列的方法注册到meppedStatements中，那么究竟是如何注入的呢？流程又是怎么样的？下面我们将一起来分析下。

在MP中，ISqlInjector负责SQL的注入工作，它是一个接口，AbstractSqlInjector是它的实现类，实现关系如下：

1556433826583

在AbstractSqlInjector中，主要是由inspectInject()方法进行注入的，如下：

@Override
public void inspectInject(MapperBuilderAssistant builderAssistant, Class<?> mapperClass) {
    Class<?> modelClass = extractModelClass(mapperClass);
    if (modelClass != null) {
        String className = mapperClass.toString();
        Set<String> mapperRegistryCache = GlobalConfigUtils.getMapperRegistryCache(builderAssistant.getConfiguration());
        if (!mapperRegistryCache.contains(className)) {
            List<AbstractMethod> methodList = this.getMethodList();
            if (CollectionUtils.isNotEmpty(methodList)) {
                TableInfo tableInfo = TableInfoHelper.initTableInfo(builderAssistant, modelClass);
                // 循环注入自定义方法
                methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo));
            } else {
                logger.debug(mapperClass.toString() + ", No effective injection method was found.");
            }
            mapperRegistryCache.add(className);
        }
    }
}

在实现方法中，methodList.forEach(m -> m.inject(builderAssistant, mapperClass, modelClass, tableInfo));是关键，循环遍历方法，进行注入。

最终调用抽象方法injectMappedStatement进行真正的注入：

    /**
     * 注入自定义 MappedStatement
     *
     * @param mapperClass mapper 接口
     * @param modelClass  mapper 泛型
     * @param tableInfo   数据库表反射信息
     * @return MappedStatement
     */
    public abstract MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo);

查看该方法的实现：

1556434252779

以SelectById为例查看：

public class SelectById extends AbstractMethod {

    @Override
    public MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
        SqlMethod sqlMethod = SqlMethod.LOGIC_SELECT_BY_ID;
        SqlSource sqlSource = new RawSqlSource(configuration, String.format(sqlMethod.getSql(),
            sqlSelectColumns(tableInfo, false),
            tableInfo.getTableName(), tableInfo.getKeyColumn(), tableInfo.getKeyProperty(),
            tableInfo.getLogicDeleteSql(true, false)), Object.class);
        return this.addSelectMappedStatement(mapperClass, sqlMethod.getMethod(), sqlSource, modelClass, tableInfo);
    }
}

可以看到，生成了SqlSource对象，再将SQL通过addSelectMappedStatement方法添加到meppedStatements中。

1556435280979

public abstract MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo);


查看该方法的实现：

 [外链图片转存中...(img-7KAuG7HQ-1573778210222)]

以SelectById为例查看：

```java
public class SelectById extends AbstractMethod {

    @Override
    public MappedStatement injectMappedStatement(Class<?> mapperClass, Class<?> modelClass, TableInfo tableInfo) {
        SqlMethod sqlMethod = SqlMethod.LOGIC_SELECT_BY_ID;
        SqlSource sqlSource = new RawSqlSource(configuration, String.format(sqlMethod.getSql(),
            sqlSelectColumns(tableInfo, false),
            tableInfo.getTableName(), tableInfo.getKeyColumn(), tableInfo.getKeyProperty(),
            tableInfo.getLogicDeleteSql(true, false)), Object.class);
        return this.addSelectMappedStatement(mapperClass, sqlMethod.getMethod(), sqlSource, modelClass, tableInfo);
    }
}
```

可以看到，生成了SqlSource对象，再将SQL通过addSelectMappedStatement方法添加到meppedStatements中。

![在这里插入图片描述](https://imgconvert.csdnimg.cn/aHR0cDovL3d3dy5wYnRlYWNoLmNvbS9wb3N0L2phdmFfZGlzdHJpYnV0L215YmF0aXMtcGx1cy0wMS8xNTU2NDM1MjgwOTc5LnBuZw?x-oss-process=image/format,png)

本文内容由网友自发贡献，版权归原作者所有，本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容，请联系:hwhale#tublm.com(使用前将#替换为@)

Java开发框架

MyBatis

MyBatisPlus