Mybatis 33_select元素和@Select注解 项目0408@Select

select元素和@Select注解

元素通常用于定义一条Select语句。需要指定如下两个属性：
- id ：SQL语句的唯一标识。需要与Mapper接口的方法名相同。
- resultType或resultMap： resultType指定结果集每行记录映射对象类型（同名映射）。
resultMap需要定义专门的映射规则。

如果你用@Select注解，id不需要（直接修饰Mapper接口的方法）。
resultType也不需要（MyBatis可通过方法返回值类型来推断出每行记录映射对象类型）

resultMap - 对应@Results注解。

元素还支持大量的额外属性，如果使用@Select注解，需要配置@Options注解来指定这些额外的属性。

项目0408@Select

主类

package lee;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.itcheng.app.dao.NewsMapper;
import org.itcheng.app.domain.News;

public class NewsManager
{
	// SqlSessionFactory应该是应用级别
	private static SqlSessionFactory sqlSessionFactory;
	public static void main(String[] args) throws IOException
	{
		String resource = "mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		// 1. 创建SqlSessionFactory
		sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
		// 2. 打开SqlSession
		SqlSession sqlSession = sqlSessionFactory.openSession();
		
		// 保存消息
//		saveNews(sqlSession);
		/*
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.saveNews ==>  Preparing: insert into news_inf values (null, ?, ?) 
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.saveNews ==> Parameters: 测试标题(String), 测试内容(String)
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.saveNews <==    Updates: 1
		 * 
		 * */
		
		// 更新消息
//		updateNews(sqlSession);	
        /* DEBUG [main] org.itcheng.app.dao.NewsMapper.updateNews ==>  Preparing: update news_inf set news_title = ?, news_content = ? where news_id=? 
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.updateNews ==> Parameters: 修改的标题(String), 修改的内容(String), 1(Integer)
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.updateNews <==    Updates: 1
         * */
		
		// 删除消息
//		deleteNews(sqlSession);			
        /* DEBUG [main] org.itcheng.app.dao.NewsMapper.deleteNews ==>  Preparing: delete from news_inf where news_id = ? 
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.deleteNews ==> Parameters: 2(Integer)
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.deleteNews <==    Updates: 1
         * */
		
		// 查询消息
		selectNews(sqlSession);		
        /* class com.sun.proxy.$Proxy23
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.findNews ==>  Preparing: select news_id id, news_title title, news_content content from news_inf where news_id > ? 
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.findNews ==> Parameters: -1(Integer)
		 * DEBUG [main] org.itcheng.app.dao.NewsMapper.findNews <==      Total: 8
		 * [News [id=1, title=修改的标题, content=修改的内容], News [id=3, title=22, content=2222222222222], News [id=4, title=33, content=3333333333333], News [id=5, title=44, content=4444444444444], News [id=6, title=55, content=5555555555555], News [id=7, title=66, content=6666666666666], News [id=8, title=77, content=7777777777777], News [id=9, title=测试标题, content=测试内容]]
         * */
	}
	
	public static void saveNews(SqlSession sqlSession)
	{
		News news = new News(null, "测试标题", "测试内容");
		
		NewsMapper newsMapper = sqlSession.getMapper(NewsMapper.class);
		
		newsMapper.saveNews(news);
		
		// 4. 提交事务
		sqlSession.commit();
		// 5. 关闭资源
		sqlSession.close();	
	}
	
	public static void updateNews(SqlSession sqlSession)
	{

		News news = new News(1, "修改的标题", "修改的内容");
		
		NewsMapper newsMapper = sqlSession.getMapper(NewsMapper.class);
		
		newsMapper.updateNews(news);
		
		// 4. 提交事务
		sqlSession.commit();
		// 5. 关闭资源
		sqlSession.close();	
	
	}
	
	public static void deleteNews(SqlSession sqlSession)
	{
		
		// SqlSession的insert、update、delete方法都只是去执行DML语句
		// 因此这个三个方法并没有本质的区别：它们都只是调用PreparedStatement的executeUpdate()方法来执行DML语句。
		
		NewsMapper newsMapper = sqlSession.getMapper(NewsMapper.class);
		newsMapper.deleteNews(2);
		
		// 4. 提交事务
		sqlSession.commit();
		// 5. 关闭资源
		sqlSession.close();	
	}
	
	public static void selectNews(SqlSession sqlSession)
	{
		// 此处的NewsMapper只是一个接口
		// MyBatis会使用JDK的动态代理为Mapper接口生成实现类
		NewsMapper newsMapper = sqlSession.getMapper(NewsMapper.class);
		System.out.println(newsMapper.getClass());
		List<?> list = newsMapper.findNews(-1);
		
		System.out.println(list);
		
		// 4. 提交事务
		sqlSession.commit();
		// 5. 关闭资源
		sqlSession.close();	
	}	
		
}

接口类，使用注解，由于使用注解所以代替了mapper映射文件。

package org.itcheng.app.dao;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;
import org.itcheng.app.domain.News;

// Mapper组件相当于DAO组件
public interface NewsMapper
{
	@Insert("insert into news_inf values (null, #{title}, #{content})")
	int saveNews(News news);
	
	@Update("update news_inf set news_title = #{title}, news_content = #{content} " 
		 + "where news_id=#{id}")
	int updateNews(News news);
	
	@Delete("delete from news_inf where news_id = #{xyz}")
	void deleteNews(Integer id);
	
	// 当使用@Select注解时，无需指定resultType属性，因为MyBatis可根据List返回值类型来推断
	@Select("select news_id id, news_title title, news_content content "
		+ "from news_inf where news_id > #{id}")
	List<News> findNews(Integer id);
}

主配置文件

DOCTYPE configuration
	PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
	"http://mybatis.org/dtd/mybatis-3-config.dtd">
	
<configuration>

 	<typeAliases>
 		
 		<package name="org.itcheng.app.domain"/>
 	typeAliases>
 	
	
	<environments default="mysql">
		
		<environment id="mysql">
			
			<transactionManager type="JDBC" />
			
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			dataSource>
		environment>
	environments>
	<mappers>
		
		<mapper class="org.itcheng.app.dao.NewsMapper" />
	mappers>

configuration>