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：
在这里插入图片描述

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：

    @Testpublic void testInsert() throws IOException {//使用文件流读取核心配置文件SqlMapConfig.xmlInputStream 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sqlSessionsqlSession.close();}

测试结果：
在这里插入图片描述

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：

    @Testpublic void testInsert() throws IOException {//使用文件流读取核心配置文件SqlMapConfig.xmlInputStream 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sqlSessionsqlSession.close();}