Mybatis知识小汇（2）——实现增删改查

增删改查

增删该由事务的提交

1. namespace:命名空间中的包要和接口一致

2. select：表示查询语句

   • id：表示实现的方法名
   • resultType：表示返回值的类型
   • parameterType：表示参数类型

3. UserMapper

   ```java
   

   public interface UserMapper {
   //获取用户列表
   List getUserList();
   //更加id查询用户
   User getUserById(int id);
   //增加一个用户
   int addUser(User user);
   //修改一个用户
   int updateUser(User user);
   //删除一个用户
   int deleteUser(int id);
   }
   ```

4. UserMapper.xml

<?xml version="1.0" encoding="utf8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--namespace绑定对应的接口-->
<mapper namespace="com.wjq.dao.UserMapper">
<!--    select查询语句-->
    <select id="getUserList" resultType="com.wjq.pojo.User">
        select * from user;
    </select>

    <select id="getUserById" parameterType="int" resultType="com.wjq.pojo.User">
        select * from user where id = #{id};
    </select>

    <insert id="addUser" parameterType="com.wjq.pojo.User">
        insert into user (id,name,pwd) values (#{id}, #{name}, #{pwd});
    </insert>

    <update id="updateUser" parameterType="com.wjq.pojo.User" >
        update user set name = #{name}, pwd = #{pwd} where id = #{id};
    </update>

    <delete id="deleteUser" parameterType="int">
        delete from user where id = #{id};
    </delete>
</mapper>

3. UserMapperTest

public class UserMapperTest {
    @Test
    public void testUserLIst(){
        //获取SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //获取UserMapper对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = userMapper.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        //关闭
        sqlSession.close();
    }

    @Test
    public void testUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1);
        System.out.println(user);
        sqlSession.close();
    }
    @Test
    public void addUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int num = mapper.addUser(new User(4, "田七", "444444"));
        if (num > 0){
            System.out.println("ok");
        }
        //提交事务
        sqlSession.commit();
        sqlSession.close();

    }
    @Test
    public void updateUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.updateUser(new User(4, "aa", "555555"));
         //提交事务
        sqlSession.commit();
        sqlSession.close();

    }
    @Test
    public void deleteUser(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(4);
         //提交事务
        sqlSession.commit();
        sqlSession.close();

    }
}

万能的Map

当数据库中的表、字段、参数过多时，可以考虑使用map

1. UserMapper

       int addUser2(Map<String, Object> map);
   

2. UserMapper.xml

   <insert id="addUser2" parameterType="map">
       insert into user (id,name) values (#{userId}, #{userName});
   </insert>
   

3. UserMapperTest

   @Test
   public void addUserMap(){
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       Map map = new HashMap<String, Object>();
       //需要什么添加什么
       map.put("userId", 6);
       map.put("userName", "map");
       mapper.addUser2(map);
       sqlSession.commit();
       sqlSession.close();
   }
   

• Map传递参数时，直接从key中取值【parameterType=“map”】
• 对象传递时，直接获取对象的属性【parameterType=“User”】
• 当为一个基本数据类型时，可以省略【parameterType=“int”】
• 当为多个参数时，用map或者注解

模糊查询

1. UserMapper

   //模糊查询获取用户
   List<User> getUserLike(String value);
   
   List<User> getUserLike2(String value);
   

2. UserMapper.xml

   <!--模糊查询获取用户-->
   <select id="getUserLike" parameterType="String" resultType="com.wjq.pojo.User">
       select * from user where name like #{value};
   </select>
   <!--直接在sql中使用拼接-->
   <select id="getUserLike2" parameterType="String" resultType="com.wjq.pojo.User">
       select * from user where name like "%"#{value}"%";
   </select>
   

3. UserMapperTest

   @Test
   public void getUserLike(){
       SqlSession sqlSession = MybatisUtils.getSqlSession();
       UserMapper mapper = sqlSession.getMapper(UserMapper.class);
       List<User> userList = mapper.getUserLike("%张%");//推荐这种
       for (User user : userList) {
           System.out.println(user);
       }
       System.out.println("---------------------------------");
       List<User> userLike2 = mapper.getUserLike2("张");
       for (User user : userLike2) {
           System.out.println(user);
       }
       sqlSession.close();
   }
   

上一节—>简介、第一个Mybatis

如有不对的地方欢迎指出，共同进步！

标签：mapper,小汇,改查,UserMapper,sqlSession,user,Mybatis,id,User
来源： https://blog.csdn.net/weixin_45734378/article/details/113761166