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MyBatisPlus

• 一、快速入门
• • 1.1 引入MyBatisPlus起步依赖
  • 1.2 自定义的Mapper继承MyBatisPlus的BaseMapper接口
  • 1.3 对比Mybatis
  • 1.4 MyBatisPlus的增删改查方法
• 二、MyBatisPlus常用注解
• • 2.1 MyBatisPlus常用注解如下
• 三、MyBatisPlus常用配置

一、快速入门

1.1 引入MyBatisPlus起步依赖

<dependency>
  <groupId>com.baomidou</groupId>
  <artifactId>mybatis-plus-boot-starter</artifactId>
  <version>3.4.2</version>
</dependency>

1.2 自定义的Mapper继承MyBatisPlus的BaseMapper接口

public interface UserMapper extends BaseMapper<User> {
}

1.3 对比Mybatis

• 要操作的数据库表结构：

create table user
(
    id      int not null primary key,
    account int null
);

• Mybatis的UserMapper.java:

public interface UserMapper {
    int insert(User row);

    int insertSelective(User row);

    User selectByPrimaryKey(Integer id);

    int updateByPrimaryKeySelective(User row);

    int updateByPrimaryKey(User row);
}

• Mybatis的UserMapper .xml：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.demo.mapper.UserMapper">
  <resultMap id="BaseResultMap" type="com.demo.po.User">
  </resultMap>
  <sql id="Base_Column_List">
    id, account
  </sql>
  <select id="selectByPrimaryKey" parameterType="java.lang.Integer" resultMap="BaseResultMap">
    select 
    <include refid="Base_Column_List" />
    from user
    where id = #{id,jdbcType=INTEGER}
  </select>
  <insert id="insert" parameterType="com.demo.po.User">
    insert into user (id, account)
    values (#{id,jdbcType=INTEGER}, #{account,jdbcType=INTEGER})
  </insert>
  <insert id="insertSelective" parameterType="com.demo.po.User">
    insert into user
    <trim prefix="(" suffix=")" suffixOverrides=",">
      <if test="id != null">
        id,
      </if>
      <if test="account != null">
        account,
      </if>
    </trim>
    <trim prefix="values (" suffix=")" suffixOverrides=",">
      <if test="id != null">
        #{id,jdbcType=INTEGER},
      </if>
      <if test="account != null">
        #{account,jdbcType=INTEGER},
      </if>
    </trim>
  </insert>
  <update id="updateByPrimaryKeySelective" parameterType="com.demo.po.User">
    update user
    <set>
      <if test="account != null">
        account = #{account,jdbcType=INTEGER},
      </if>
    </set>
    where id = #{id,jdbcType=INTEGER}
  </update>
  <update id="updateByPrimaryKey" parameterType="com.demo.po.User">
    update user
    set account = #{account,jdbcType=INTEGER}
    where id = #{id,jdbcType=INTEGER}
  </update>
</mapper>

• MyBatisPlus只需UserMapper.java继承 BaseMapper<>即可：

public interface UserMapper extends BaseMapper<User> {
}

1.4 MyBatisPlus的增删改查方法

@SpringBootTest
class DemoApplicationTests {

    @Autowired
    private UserMapper userMapper;

    @Test
    void testInsert() {
        User user = new User();
        user.setId(5);
        user.setAccount(2000);
        userMapper.insert(user);
    }

    @Test
    void testSelectById() {
        User user = userMapper.selectById(5);
        System.out.println(user);
    }

    @Test
    void testUpdateById() {
        User user = new User();
        user.setId(5);
        user.setAccount(8000);
        userMapper.updateById(user);
    }

    @Test
    void testDeleteById() {
        userMapper.deleteById(5);
    }

}

二、MyBatisPlus常用注解

• 类名驼峰转下划线作为表名
• 名为id的字段作为主键
• 变量名驼峰转下划线作为表的字段名

2.1 MyBatisPlus常用注解如下

• @TableName：用来指定表名
• @TableId：用来指定表中的主键字段信息
• @TableFiled：用来指定表中的普通字段信息

三、MyBatisPlus常用配置

mybatis-plus:
  type-aliases-package: com.demo.po
  mapper-locations: classpath*:mapper/**/*.xml  # 默认
  global-config:
    db-config:
      id-type: auto # id类型自增长