MyBatis 实现主键回写

当我们向数据库插入数据时，主键是设置的自增的，但是我们插入好数据库后，我们希望得到刚刚插入的数据的主键，mybatis可以实现这样的功能
应用场景：
员工与部门，当新员工进公司，该员工肯定属于某个部门，插入数据的时候，要告诉部门表，这个员工属于哪个部门

数据库表

mapper.xml文件代码

<mapper namespace="UserDaoMapper">

    
    <insert id="saveUser" useGeneratedKeys="true" keyColumn="id" keyProperty="id">
        INSERT INTO tb_user (
            user_name,
            password,
            name,
            age,
            sex,
            birthday,
            created,
            updated
        )
        VALUES(
            #{userName},
            #{password},
            #{name},
            #{age},
            #{sex},
            #{birthday},
            NOW(),
            NOW()
        )
    insert>
mapper>

mybatis-config.xml文件代码

<configuration>
    
  <properties resource="jdbc.properties"  />

  <settings>
  
    <setting name="mapUnderscoreToCamelCase" value="true" />
  settings>
  <typeAliases>
    
    <package name="cn.itcast.domain"/>
  typeAliases>
    <environments default="development" >
        <environment id="development">
            <transactionManager type="JDBC" />
            <dataSource type="POOLED">
                
                <property name="driver" value="${jdbc.driverClass}" />
                
                <property name="url" value="${jdbc.url}" />
                
                <property name="username" value="${jdbc.username}" />
                
                <property name="password" value="${jdbc.password}" />
            dataSource>
        environment>
    environments>
    
    <mappers>
        <mapper resource="UserDaoMapper.xml"/>
    mappers>
configuration>

jdbc.properties文件

jdbc.driverClass=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis
jdbc.username=root
jdbc.password=123

Test测试类

public class UserDaoTest {
    private SqlSession sqlSession;

    @Before
    public void setUp() throws IOException {
        // 加载mybatis-config.xml文件
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
        // 创建sqlSessionFactory的构造器
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        // 创建sqlSession工厂
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        // 通过工厂生成sqlSession
        sqlSession = sqlSessionFactory.openSession();

    }
    @Test
    /**
     * 插入用户信息
     * @throws IOException
     */
    public void inserUser() throws IOException {
        UserDao dao = new UserDaoImpl(sqlSession);
        User user =new User();
        user.setUserName("jiumozhi");
        user.setPassword("123456");
        user.setName("鸠摩智");
        user.setAge(30);
        user.setSex(1);
        user.setBirthday(new Date());
        dao.saveUser(user);

        System.out.println(user);

    }
}

dao层方法

@Override
    public void saveUser(User user) {
        sqlSession.insert("UserDaoMapper.saveUser", user);
        sqlSession.commit();
        sqlSession.close();
    }

展示结果