一、常用注解

增删改查

@Insert

@InsertProvideInsert

@Delete

@DeleteProvideDelete

@Update

@UpdataProvideUpdate

@Select

@SelectProviderSelect

@xxx 实现增删改查

@xxxProvidexxx 实现动态的增删改查

映射

@Results 多个结果映射，包含多个@Result

@Result 单个结果映射

@One 一对一的复杂映射，必须指定select属性

@Maney 集合属性的复杂映射，必须指定select属性

@Param 对mapper接口中方法参数的注解

配置选项

@Option 配置附加功能，如对某语句设置二级缓存

二、具体使用

注解实现增删改查

使用注解时在xml文件中不需要写对应的语句

//mapper接口中对方法使用注解
public interface UserMapper {
    @Select("select * from tb_user where id = #{id}")
   public List<User> selectbyid(@Param("id") Integer id);
}

<!--mapper.xml文件中-->
<?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.wj.dao.mapper.UserMapper">
<cache eviction="FIFO" flushInterval="60000" size="512" readOnly="true"/>
<!--不写对应的select语句-->
</mapper>

public interface UserMapper {
    //查
    @Select("select * from tb_user where id = #{id}")
   public User selectbyid(@Param("id") Integer id);
    //增
    @Insert("insert into tb_user (id,userCode,userName,userPassword,gender,birthday," +
            "email,phone,address,userDesc,userRole,imgPath,createdBy,creationDate," +
            "modifyBy) values (#{id},#{userCode},#{userName},#{userPassword},#{gender}," +
            "#{birthday},#{email},#{phone},#{address},#{userDesc},#{userRole},#{imgPath}," +
            "#{createdBy},#{creationDate},#{modifyBy})")
    public int adduser(User user);
    //改
    @Update("update tb_user set userPassword = #{userPassword} where id = #{id}")
    public int modifybyid(@Param("id") Integer id,@Param("userPassword") String pw);
    //删
    @Delete("delete from tb_user where userName=#{userName}")
    public int deleteuserbyname(@Param("userName") String name);
}

注解实现动态增删改查

@xxxProvidxxx注解有两个属性 type和method

type指定提供动态语句方法的类，method指定类中的方法

动态查询语句的使用

首先创建工具类

package com.wj.util;

import org.apache.ibatis.jdbc.SQL;
import java.util.Map;
import java.util.Objects;

/**
 * @Description:
 * @Author WJ
 * @Date 2023/2/16:17:26
 * @Version V1.0
 **/
public class UserDynaSqlProvide {
    public String getUserList(final Map<String, Objects> para){

        return new SQL(){
            {
                SELECT("*");
                FROM("tb_user");
                if (null != para.get("userName") && !"".equals(para.get("userName"))) {
                    WHERE("userName like concat('%',#{userName},'%')");
                }
                if (null != para.get("userPassword") && !"".equals(para.get("userPassword"))){
                    WHERE("userPassword = #{userPassword}");
                }
            }
        }.toString();
    }
}

创建接口方法，添加注解

 @SelectProvider(type = UserDynaSqlProvide.class,method = "getUserList")
    public List<User> selectbynameandpws(@Param("userName") String name,@Param("userPassword") String pws);

在provide类中使用字符串拼接sql语句非常困难，所以mybatis提供了工具类来构造sql语句，常用的方法如下图

注解实现复杂映射

pojo中

package com.wj.dao.pojo;

import lombok.Data;
import lombok.Getter;
import lombok.Setter;
import lombok.ToString;

/**
 * @Description:
 * @Author WJ
 * @Date 2023/2/14:09:16
 * @Version V1.0
 **/
@Setter
@Getter
@ToString
public class IdCard {
    private Integer id;     //id
    private Integer uid;    //用户id
    private String code;    //身份证号码
    private User   user;    //一对一
}

public interface IdCardMapper {
    @Select("select * from tb_idcard where id in(#{id1},#{id2})")
    @Results({
    		//指定主键
            @Result(id = true,column = "id",property = "id"),
            //用id的值传入selectbyid的方法，值返回给idcard的user对象
            @Result(column = "id" ,property = "user",
            one=@One(select = "com.wj.dao.mapper.UserMapper.selectbyid")
            )
    })
    public List<IdCard> findCodeById(@Param("id1") Integer id1,@Param("id2") Integer id2);
}

测试

 @Test
    public void select_all() throws IOException {
        try (SqlSession sqlSession = MybatisUtil.createSqlsession()) {
            IdCardMapper mapper = sqlSession.getMapper(IdCardMapper.class);
           ;
            for (IdCard idCard: mapper.findCodeById(3,4)) {
                System.out.println(idCard);
            }

        }
    }

结果



若是pojo中嵌套的对象是单个，就使用@one，若嵌套的是列表，就用@Maney，需要注意的是一对一，则@One指定select语句返回的是对象，多对多则@Maney指定的select语句返回的是List