概述
本文介绍根据id查询一条记录，模糊查询，查询count()函数
根据id查询一条记录
修改IUserMapper
增加下面代码：
@Select("select id,username,password,age,sex,status from user where id=#{id}")
public User queryById(String id);
注解中的sql语句，与 mapper.xml 中的写法是一样的
由于只传入 一个基本数据类型，所以在sql中 #{id}可以写成任意值，如：#{aaa}也是可以的，但代码规范不允许这么写
测试
@org.junit.Test
public void test3() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
IUserMapper mapper = sqlSession.getMapper(IUserMapper.class);
User u=mapper.queryById("10001");
String info = String.format("id：%s,用户名：%s", u.getId(), u.getUsername());
System.out.println(info);
sqlSession.close();
inputStream.close();
}
模糊查询
修改IUserMapper
增加下面代码：
@Select("select id,username,password,age,sex,status from user where username like #{username}")
public List<User> queryByName(String username);
测试
@org.junit.Test
public void test5() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
IUserMapper mapper = sqlSession.getMapper(IUserMapper.class);
List<User> list=mapper.queryByName("李%");
for(User u:list) {
String info = String.format("id：%s,用户名：%s", u.getId(), u.getUsername());
System.out.println(info);
}
sqlSession.close();
inputStream.close();
}
查询count()
修改IUserMapper
增加下面代码：
@Select("select count(id) from user where sex = #{sex}")
public int queryCountBySex(String sex);
由于查询 count() 函数，所有返回 int 型
测试
@org.junit.Test
public void test6() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
IUserMapper mapper = sqlSession.getMapper(IUserMapper.class);
int count=mapper.queryCountBySex("1");
System.out.println("男生有"+count+"人！");
sqlSession.close();
inputStream.close();
}