这篇文章介绍了MyBatis的主键返回方法

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一.需求分析

当我们表的主键设置为自增，且插入数据后需要主键id时，就要使用主键返回的方法，来获取当前插入数据的主键。
表如下：

二.主键返回

1.使用selectKey 标签

< selectKey >标签,keyProperty：设置为目标属性，resultType：设置返回值类型，order:值为after,before
after: sql之后执行，before: sql之前执行

示例:
StudentMapper接口

public interface StudentMapper {    int insert(Student student);}

StudentMapper.xml代码

    <insert id="insert" parameterType="com.hem.pojo.Student">        <selectKey keyProperty="id" resultType="int" order="AFTER">            select last_insert_id()        </selectKey>        insert into student (name,email,age)        values (#{name},#{email},#{age});    </insert>

test代码：

    @Test    public void testInsert() throws IOException {        //使用文件流读取核心配置文件SqlMapConfig.xml        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");        //创建SqlSessionFactory工厂        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);        //取出sqlSession对象        SqlSession sqlSession = factory.openSession();        //完成查询操作        StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);        Student student = new Student("小白","12321",99);        int num = studentMapper.insert(student);        System.out.println(student.getId());        sqlSession.commit();        //关闭sqlSession        sqlSession.close();    }

测试结果：

2. 设置< insert >便签的属性

设置 useGeneratedKeys=”true”，然后再把 keyProperty 设置为目标属性就 OK 了

示例:
StudentMapper接口

public interface StudentMapper {    int insert(Student student);}

StudentMapper.xml代码：

<insert id="insert" parameterType="com.hem.pojo.Student" useGeneratedKeys="true" keyProperty="id">        insert into student (name,email,age)        values (#{name},#{email},#{age});    </insert>

test代码：

    @Test    public void testInsert() throws IOException {        //使用文件流读取核心配置文件SqlMapConfig.xml        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");        //创建SqlSessionFactory工厂        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(in);        //取出sqlSession对象        SqlSession sqlSession = factory.openSession();        //完成查询操作        StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);        Student student = new Student("小白","12321",99);        int num = studentMapper.insert(student);        System.out.println(student.getId());        sqlSession.commit();        //关闭sqlSession        sqlSession.close();    }

测试结果：

202210161704日

来源地址：https://blog.csdn.net/qq_53843555/article/details/127347086