I'm all you paranoid and greedy, came from my love for you twenty-four hours full to the brim.

1、namespace

Package name to the namespace and Dao / mapper interface is consistent package name

2、select

Select query

id: is the method name in the corresponding namespace
resultType: Returns the value of SQL statements executed
parameterType: Parameter Type

Write Interface

package com.rui.dao;

import com.rui.pojo.User;

import java.util.List;

public interface UserMapper {
    //根据id查询用户
    User getUserById(int id);
}

Corresponding write mapper sql statement

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

test

@Test
public void getUserById(){
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    User user = mapper.getUserById(1);
    System.out.println(user);
    sqlSession.close();
}

3、Insert

4、Update

5、Delete

6, error analysis

Labels do not match error
resource binding mapper, need to use the path
Configuration file must meet specifications
NullPointException, is not registered with resources
Chinese garbage problem in the xml file output
maven resource does not export issues

7, Universal Map

Assuming that too much of our entity class, or database tables, fields or parameters, we should consider using the Map

//万能Map
int addUser2(Map<String,Object> map);

<!--对象中的属性，可以直接取出来 parameterType=传递map中的key-->
<insert id="addUser2" parameterType="map">
    insert into mybatis.user (id, name, pwd) values (#{userId},#{userName},#{password});
</insert>

//万能map
@Test
public void addUser2(){
    SqlSession sqlSession = MyBatisUtils.getSqlSession();
    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    HashMap<String, Object> map = new HashMap<>();
    map.put("userId",4);
    map.put("userName","王五");
    map.put("password","23333");
    mapper.addUser2(map);
    //提交事务
    sqlSession.commit();
    sqlSession.close();
}

Map transmission parameters, taken directly to key in the sql. [ParameterType = "map"]

Objects are passed parameters, take the objects directly sql attribute. [ParameterType = "Object"]

Only a case where the basic type parameter, can be directly taken to the sql

Multiple parameters Map, or notes

8, fuzzy query

Java code is executed when the transfer wildcard %%
```
List<User> userList=mapper.getUserLike("%李%");
```

Use wildcards in sql mosaic

select * from mybatis.user where name like "%"#{value}"%"

MyBatis - Crude