mybatis详解-(8)配置自增主键

╰半橙微兮° 2022-06-06 01:28 156阅读 0赞

延续上一篇增删改查，在添加的时候使用的是数据库的自增主键，如果换成oracle这种没有自增主键的就无法实现，并且保存完成之后，在程序中是获取不到对象id的。我们打印保存后的对象如下：

# 1.未配置主键自增 #

@Test
        public void testMybatisAdd() {
       //测试添加
                SqlSessionFactory sqlSessionFactory = null;
                SqlSession sqlSession = null;
                try {
                    sqlSessionFactory = getSqlSessionFactory();
                    //openSession可以添加参数，无参数表示不会自动提交，需要手动提交
                    sqlSession = sqlSessionFactory.openSession();
    // sqlSession = sqlSessionFactory.openSession(true);
    
                    EmployeeMapper mapper = sqlSession.getMapper(EmployeeMapper.class);
    
                    Employee employee = new Employee();
                    //数据库设置id自增
                    employee.setLastName("huanan");
                    employee.setEmail("tang_man@sina.com");
                    employee.setGender("2");
    
                    mapper.addEmployee(employee);
    
                    System.out.println(employee);
    
                    sqlSession.commit();
    
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    sqlSession.close();
                }
        }

> DEBUG - ooo Using Connection \[com.mysql.jdbc.JDBC4Connection@184f6be2\]  
> DEBUG - ==> Preparing: insert into mybatis\_employee (last\_name,email,gender) values (?,?,?);  
> DEBUG - ==> Parameters: huanan(String), tang\_man@sina.com(String), 2(String)  
> Employee \[id=null, lastName=huanan, email=tang\_man@sina.com, gender=2\]

这里打印的id=null，mybatis可以通过配置，自动生成主键

# 2.配置主键自增 #

在`insert` 标签中添加两个值  
useGeneratedKeys=”true”表示使用自增主键  
keyProperty=”id”表示id为自增主键

<insert id="addEmployee" parameterType="org.mybatis.crud.Employee" useGeneratedKeys="true" keyProperty="id">
            insert into mybatis_employee 
            (last_name,email,gender) 
            values 
            (#{lastName},#{email},#{gender});
        </insert>

再次测试添加方法，可以获取到主键的值id=7

> DEBUG - ooo Using Connection \[com.mysql.jdbc.JDBC4Connection@1f7030a6\]  
> DEBUG - ==> Preparing: insert into mybatis\_employee (last\_name,email,gender) values (?,?,?);  
> DEBUG - ==> Parameters: hussanan(String), tang\_@qq.com(String), 2(String)  
> Employee \[id=7, lastName=hussanan, email=tang\_@qq.com, gender=2\]

# 3.不存在自增主键数据库如何配置 #

<insert id="addEmployeeo">
            
            <selectKey keyProperty="id" order="BEFORE" resultType="Integer">
                select employees_seq.nextval from dual;
            </selectKey>
    
            insert into mybatis_employee 
            (id,last_name,email,gender) 
            values 
            (#{id},#{lastName},#{email},#{gender});
        </insert>