在Mybatis中，实体类的属性需要与数据库字段一一映射;
使用对象传值时，
$1.$ SQL语句#{}中的参数名需要与实体类属性名保持一致；
$2.$ SQL语句中的字段个数需要与实体类的构造方法参数个数相同；
所以说用对象传值时有实体类的约束。

使用map传值，在SQL语句中可以自定义字段名，以及字段的个数
map传值通过键值对关联字段，就去除了实体类的约束；

字段个数设置有个前提：数据库中设置字段允许为空；

insert

<mapper namespace="com.tl.dao.UserMapper">
    <insert id="addUser" parameterType="map">
    insert into user(id,name) values (#{uid},#{pename});
    </insert>
</mapper>

public class Test {
    @org.junit.Test
        public void Test() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("uid",7);
        map.put("pename","唐僧");
        int i = mapper.addUser(map);
        System.out.println(i);
        sqlSession.commit();
        sqlSession.close();
    }
}

update

<?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.tl.dao.UserMapper">
    <update id="updateUser" parameterType="map">
    update user set name=#{pename} where id=#{uid};
    </update>
</mapper>

public class Test {
    @org.junit.Test
        public void Test() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        HashMap<String, Object> map = new HashMap<String, Object>();
        map.put("uid",7);
        map.put("pename","至尊宝");
        int i = mapper.updateUser(map);
        System.out.println(i);
        sqlSession.commit();
        sqlSession.close();
    }
}

前一篇：07-Mybatis参数的使用之二–多个参数的使用@Param
https://blog.csdn.net/fsjwin/article/details/109669306
对象传值，传入的是一个对象，比较点单，直接看栗子。

1. StudentDao

 /**
     *  通过name和age寻找学生
     *
     */
    public List<Student> selectStudentByObject(Student student);

2. StudentDao.xml

    <!--传递一个对象过来-->
    <select id="selectStudentByObject"  resultType="com.yuhl.domain.Student">
        select id,name,email,age from student where name =#{name} or age =#{age}
    </select>

3.测试

 @Test
    public void test5() throws IOException {
        SqlSession sqlsession = MybatisUtil.getSqlsession();
        StudentDao studentDao = sqlsession.getMapper(StudentDao.class);
        //可以吧查询的条件放进去，也可以使用一个单独的类ParaObject类封装就可以了。
        Student student = new Student(1001, "yuhl", "ss.qq.com", 20);
        List<Student> studentList = studentDao.selectStudentByObject(student);
        studentList.forEach(stu -> System.out.println(stu));
    }

测试结果：

Logging initialized using 'class org.apache.ibatis.logging.stdout.StdOutImpl' adapter.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
PooledDataSource forcefully closed/removed all connections.
Opening JDBC Connection
Created connection 1739876329.
==>  Preparing: select id,name,email,age from student where name =? or age =?
==> Parameters: yuhl(String), 20(Integer)
<==    Columns: id, name, email, age
<==        Row: 1001, 张三, zhangsan@qq.com, 20
<==        Row: 1003, yuhl, yuhl@163.com, 20
<==        Row: 1004, rll, yuhl@163.com, 20
<==        Row: 1005, 大佬, yuhl@163.com, 20
<==      Total: 4
Student{id=1001, name='张三', email='zhangsan@qq.com', age=20}
Student{id=1003, name='yuhl', email='yuhl@163.com', age=20}
Student{id=1004, name='rll', email='yuhl@163.com', age=20}
Student{id=1005, name='大佬', email='yuhl@163.com', age=20}

4. 总结

这种做法也很普遍，需要掌握，也比较简单。

下一篇：09-Mybatis参数的使用之四–通过索引传值-了解https://blog.csdn.net/fsjwin/article/details/109670182