六、通过mapper接口加载映射文件

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

package com.ys.mapper;

import org.apache.ibatis.annotations.Delete;

import org.apache.ibatis.annotations.Insert;

import org.apache.ibatis.annotations.Select;

import org.apache.ibatis.annotations.Update;

import com.ys.po.User;

public interface UserMapper {

    //根据 id 查询 user 表数据

    public User selectUserById(int id) throws Exception;

    //向 user 表插入一条数据

    public void insertUser(User user) throws Exception;

    //根据 id 修改 user 表数据

    public void updateUserById(User user) throws Exception;

    //根据 id 删除 user 表数据

    public void deleteUserById(int id) throws Exception;

}

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

<?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.ys.mapper.UserMapper">

    <!-- 根据 id 查询 user 表中的数据

       id:唯一标识符，此文件中的id值不能重复

       resultType:返回值类型，一条数据库记录也就对应实体类的一个对象

       parameterType:参数类型，也就是查询条件的类型

    -->

    <select id="selectUserById"

            resultType="com.ys.po.User" parameterType="int">

        <!-- 这里和普通的sql 查询语句差不多，后面的 #{id}表示占位符，里面不一定要写id,写啥都可以，但是不要空着 -->

        select * from user where id = #{id1}

    </select>

    <!-- 根据 id 更新 user 表的数据 -->

    <update id="updateUserById" parameterType="com.ys.po.User">

        update user u

            <!-- <set>

                <if test="username != null and username != ‘‘">

                    u.username = #{username},

                </if>

                <if test="sex != null and sex != ‘‘">

                    u.sex = #{sex}

                </if>

            </set> -->

            <trim prefix="set" suffixOverrides=",">

                <if test="username != null and username != ‘‘">

                    u.username = #{username},

                </if>

                <if test="sex != null and sex != ‘‘">

                    u.sex = #{sex},

                </if>

            </trim>

         where id=#{id}

    </update>

    <!-- 向 user 表插入一条数据 -->

    <insert id="insertUser" parameterType="com.ys.po.User">

        <!-- 将插入的数据主键返回到 user 对象中

             keyProperty:将查询到的主键设置到parameterType 指定到对象的那个属性

             select LAST_INSERT_ID()：查询上一次执行insert 操作返回的主键id值，只适用于自增主键

             resultType:指定 select LAST_INSERT_ID() 的结果类型

             order:AFTER，相对于 select LAST_INSERT_ID()操作的顺序

         -->

        <selectKey keyProperty="id" resultType="int" order="AFTER">

            select LAST_INSERT_ID()

        </selectKey>

        insert into user(username,sex,birthday,address)

            value(#{username},#{sex},#{birthday},#{address})

    </insert>

    <!-- 根据 id 删除 user 表的数据 -->

    <delete id="deleteUserById" parameterType="int">

        delete from user where id=#{id}

    </delete>

</mapper>

2

3

4

5

6

7

8

9

//根据id查询user表数据

    @Test

    public void testSelectUserById() throws Exception{

        //获取mapper接口

        UserMapper userMapper = session.getMapper(UserMapper.class);

        User user = userMapper.selectUserById(1);

        System.out.println(user);

        session.close();

    }

2

3

4

5

6

<mappers>

       <!--批量加载mapper

          指定 mapper 接口的包名，mybatis自动扫描包下的mapper接口进行加载

         -->

       <package name="com.ys.mapper"/>

</mappers>