怕自己忘了复习mybtais（1）

今天我们同学第一天上班，他们写的是mybatis，但是使用的是xml写sql语句，我听到我好想不会写了呀，还得好好的复习一下，不能让自己忘记了，这可是我好不容易学来的技术哟，可花了我不少的时间了
-------对于一个转行的我来说

我还是一个有追求的：

一个好的程序员是底层走，但是大多数都是往框架走（一种人往底层走，一种人往框架走）

mybtais我编程测第一个框架orm，持久层框架（就是一个连接数据库的框架）轻量级的ORM框架
优点：MyBatis 避免了几乎所有的 JDBC 代码和手动设置参数以及获取结果集
使用连接池，用连接池来管理数据库的链接和释放资源。
mybatis框架将sql语句提取到xml配置文件中，每一次修改sql语句，只需要修改配置文
件中的语句即可，和代码无关
mybatis框架将视线关系对象映射，mybatis存在输入对象映射和输出对象映射。
缺点：
（说实话这没有好的一点的写sql语句的能力还真不好使用这个框架）

1. SQL语句的编写工作量较大，尤其是字段多、关联表多时，更是如此，对开发人员编写SQL语句的功底有一定要求。
2. SQL语句依赖于数据库，导致数据库移植性差，不能随意更换数据库。

原理

这个是mybtais的基本架构：以ecpilse为例

编写sqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
 PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
 	<!-- 使用mybatis需要的数据源和事务配置，后续如果整合spring之后，将不再需要 -->
 	<environments default="development">
 		<!-- 配置数据源和事务 -->
 		<environment id="development">
 			<!-- 配置事务管理,将事务管理交给mybatis管理 -->
 			<transactionManager type="JDBC" />
 			<!-- 配置数据源 -->
 			<dataSource type="POOLED">
 				<property name = "driver" value = "com.mysql.jdbc.Driver" />
 				<property name="url" value="jdbc:mysql://localhost:3306/mybatis?useUnicode=true&amp;characterEncoding=utf-8"/>
 				<property name="username" value="root"/>
 				<property name="password" value=""/>
 			</dataSource>
 		</environment>
 	</environments>
 	<!-- 加载**.xml配置文件 -->
 	<mappers>
 		<mapper resource="Food.xml"/>
 	</mappers>
 </configuration>
 

编写log4j.properties标签

# Global logging configuration 
log4j.rootLogger=DEBUG, stdout
# MyBatis logging configuration...
log4j.logger.org.mybatis.example.BlogMapper=TRACE
# Console output... 
log4j.appender.stdout=org.apache.log4j.ConsoleAppender 
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

编写失血模型

package model;

/**
 * @ClassName: food.java
 * @Description: 该类的功能描述
 * @version: v1.0.0
 * @author: 169986432
 * @date: 2020年10月11日 下午2:38:05 
 */
public class Food {
	private  int  id;
	private  String  last_name;
	private  String  gender;
	private  String  email;
	public Food() {
		super();
	}
	public Food(int id, String last_name, String gender, String email) {
		super();
		this.id = id;
		this.last_name = last_name;
		this.gender = gender;
		this.email = email;
	}
	/**
	 * @return the id
	 */
	public int getId() {
		return id;
	}
	/**
	 * @param id the id to set
	 */
	public void setId(int id) {
		this.id = id;
	}
	/**
	 * @return the last_name
	 */
	public String getLast_name() {
		return last_name;
	}
	/**
	 * @param last_name the last_name to set
	 */
	public void setLast_name(String last_name) {
		this.last_name = last_name;
	}
	/**
	 * @return the gender
	 */
	public String getGender() {
		return gender;
	}
	/**
	 * @param gender the gender to set
	 */
	public void setGender(String gender) {
		this.gender = gender;
	}
	/**
	 * @return the email
	 */
	public String getEmail() {
		return email;
	}
	/**
	 * @param email the email to set
	 */
	public void setEmail(String email) {
		this.email = email;
	}
	@Override
	public String toString() {
		return "Food [id=" + id + ", last_name=" + last_name + ", gender=" + gender + ", email=" + email + "]";
	}

}

`编写单个映射关系的sql.xml:Food.xml``

<?xml version="1.0" encoding="UTF-8"?> SELECT * FROM food WHERE last_anme= #{value} ``` 编写dao接口：查询的接口

public interface FoodDao {
	public Food queryProductById(String last_name) throws Exception;
}

编写dao接口的实现类：FoodImpl实现类

public class FoodDaoImpl   implements  FoodDao {
	//声明一个会话工厂
		private SqlSessionFactory factory;

		//由构造方法进行创建对象赋值
		public  FoodDaoImpl(SqlSessionFactory factory) {
			this.factory = factory;
		}

	@Override
	public Food queryProductById(String last_name) throws Exception {
		//开启会话
		SqlSession sqlSession = factory.openSession();
		Food prod = sqlSession.selectOne("test.foodAll", last_name);

		//关闭会话
		sqlSession.close();
		return prod;
	}
	
}

测试类：测试

public class Test {
		//创建dao的实现类
		
			public static void main(String[] args) throws Exception{
				String path = "SqlMapConfig.xml";
				InputStream config = Resources.getResourceAsStream(path);
				//创建一个会话工厂
				SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(config);
				
				testQuery1(factory);
			}
			
			public static void testQuery1(SqlSessionFactory factory) throws Exception {
				FoodDao dao = new FoodDaoImpl(factory);
				int id = 1;
				Food  food=dao.queryProductById("张三");
				System.out.println(food);
			}

	}

mybatis的最简单的增，删，改，查
思路：
1.导入jr包，创建xml里面配置增，删，改。查的sql语句
2.创建xml文件在SqlMapConfig.xml文件中进行配置加载
3.创建一个失血模型要跟数据库的字段一致
4.创建一个接口，接口当中包含5个方法，两个查询、增、删、改的方法。只有定义。
5.创建实现类，实现定义的接口，按照规定进行重写方法。声明工厂类对象，该对象由该类的构造方法进行赋值。
6.编写测试类，在测试类中，创建工厂对象，传递给dao的实现类。

编写xml：food.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
 PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
 "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="first">
	<!-- 根据id查询 -->
	<select id="queryId" parameterType="java.lang.Integer" resultType="model.Food">
		SELECT * FROM t_product WHERE p_id = #{p_id}
	</select>
	<!-- 根据名称模糊查询，返回多条结果集 -->
	<select id="queryName" parameterType="java.lang.String" resultType="model.Food">
		SELECT * FROM t_product WHERE name like "%${value}%"
	</select>
	<!-- 新增一条数据 -->
	<insert id="insert" parameterType="model.Food">
		INSERT INTO t_product(name,p_number,price) value(#{name},#{p_number},#{price})
	</insert>
	<!-- 根据id值更新 -->
	<update id="update" parameterType="model.Food">
		UPDATE t_product SET name = #{name} WHERE p_id = #{p_id}
	</update>
	<!-- 根据id删除 -->
	<delete id="delete" parameterType="java.lang.Integer">
		DELETE FROM t_product WHERE p_id = #{p_id}
	</delete>
</mapper>

编写xml：加载food。xml
编写接口增，删，改，查

public interface FoodDao {

	public  Food queryId(int id) throws Exception;

	public List<Food> queryName(String name) throws Exception;

	public Food insert(Food product) throws Exception;

	public int update(Food product) throws Exception;

	public int delete(int id) throws Exception;
}

编写接口的实现类

public class FoodDaoImpl   implements  FoodDao {
	//声明一个会话工厂
		private SqlSessionFactory factory;

		//由构造方法进行创建对象赋值
		public  FoodDaoImpl(SqlSessionFactory factory) {
			this.factory = factory;
		}

		@Override
		public Food queryId(int id) throws Exception {
			SqlSession sqlSession = factory.openSession();
			Food  food= sqlSession.selectOne("first.queryId", id);
			sqlSession.close();
			return food;
		}

		@Override
		public List<Food> queryName(String name) throws Exception {
			SqlSession sqlSession = factory.openSession();
			List<Food> list = sqlSession.selectList("first.queryName", name);
			sqlSession.close();
			return list;
		}

		@Override
		public Food insert(Food food) throws Exception {
			SqlSession sqlSession = factory.openSession();
			int row = sqlSession.insert("first.insert", food);
			sqlSession.commit();
			sqlSession.close();
			return  food;
		}

		@Override
		public int update(Food food) throws Exception {
			SqlSession sqlSession = factory.openSession();
			int row = sqlSession.update("first.update", food);
			sqlSession.commit();
			sqlSession.close();
			return row;
		}

		@Override
		public int delete(int id) throws Exception {
			SqlSession sqlSession = factory.openSession();
			int row = sqlSession.delete("first.delete", id);
			sqlSession.commit();
			sqlSession.close();
			return row;
		}
}

测试类：测试

public class Test {
		//创建dao的实现类
		
			public static void main(String[] args) throws Exception{
				String path = "SqlMapConfig.xml";
				InputStream config = Resources.getResourceAsStream(path);
				//创建一个会话工厂
				SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(config);
				
//				testQuery1(factory);
//				testQuery2(factory);
				testQuery3(factory);
			}
			
			public static void testQuery1(SqlSessionFactory factory) throws Exception {
				FoodDao dao = new FoodDaoImpl(factory);
				int id = 1;
				Food  food = dao.queryId(id);
				System.out.println(food);
			}

			public static void testQuery2(SqlSessionFactory factory) throws Exception {
				FoodDao dao = new FoodDaoImpl(factory);
				String name = "牛奶";
				List<Food> list = dao.queryName(name);
				System.out.println(list);
			}
		   public  static  void testQuery3(SqlSessionFactory factory) throws Exception {
			   SqlSession session = factory.openSession();
			   Food  food=session.getMapper(Food.class);
			   Food  food1=new  Food();
			   food1.setP_id(7);
			   food1.setName("阿萨姆奶茶");
			   food1.setP_number(788);
			   food1.setPrice(90);
			   food1.setAdd_time("2020-09-23 17:59:46.0");
		   } 
	}

总结：什么是mybatis、结构、一个案例

明天再来复习重点，mapper代理方式进行CRUD