1.Mybatis引见和简单使用

1.Mybatis介绍

MyBatis是支持普通SQL查询，存储过程和高级映射的优秀持久层框架。MyBatis消除了几乎所有的JDBC代码和参数的手工设置以及对结果集的检索封装。MyBatis可以使用简单的XML或注解用于配置和原始映射，将接口和Java的POJO（Plain Old Java Objects，普通的Java对象）映射成数据库中的记录.

2.mybatis快速入门

编写第一个基于mybaits的测试例子:
2.1. 添加jar包

2.2. 建库+表

2.3.添加Mybatis的配置文件conf.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>
	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC" />
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.jdbc.Driver" />
				<property name="url" value="jdbc:mysql://localhost:3306/mybatis" />
				<property name="username" value="root" />
				<property name="password" value="root" />
			</dataSource>
		</environment>
	</environments>
</configuration>

2.4. 定义表所对应的实体类

public class User {
	private int id;
	private String name;
	private int age;
    //get,set方法
}

2.5.定义操作users表的sql映射文件userMapper.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="com.atguigu.mybatis_test.test1.userMapper"> 
	<select id="getUser" parameterType="int" 
		resultType="com.atguigu.mybatis_test.test1.User">
		select * from users where id=#{id}
	</select>
</mapper>

2.6. 在conf.xml文件中注册userMapper.xml文件 

<mappers>
	<mapper resource="com/atguigu/mybatis_test/test1/userMapper.xml"/>
</mappers>

 
2.7. 编写测试代码：执行定义的select语句 

public class Test {
	public static void main(String[] args) throws IOException {
		String resource = "conf.xml"; 
		//加载mybatis的配置文件（它也加载关联的映射文件）
		Reader reader = Resources.getResourceAsReader(resource); 
		//构建sqlSession的工厂
		SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(reader);
		//创建能执行映射文件中sql的sqlSession
		SqlSession session = sessionFactory.openSession();
		//映射sql的标识字符串
		String statement = "com.atguigu.mybatis.bean.userMapper"+".selectUser";
		//执行查询返回一个唯一user对象的sql
		User user = session.selectOne(statement, 1);
		System.out.println(user);
	}
}

3. 操作users表的CRUD

3.1. XML的实现
1). 定义sql映射xml文件：

<insert id="insertUser" parameterType="com.atguigu.ibatis.bean.User">
	insert into users(name, age) values(#{name}, #{age});
</insert>

<delete id="deleteUser" parameterType="int">
	delete from users where id=#{id}
</delete>
		
<update id="updateUser" parameterType="com.atguigu.ibatis.bean.User">
	update users set name=#{name},age=#{age} where id=#{id}
</update>
		
<select id="selectUser" parameterType="int" resultType="com.atguigu.ibatis.bean.User">
	select * from users where id=#{id}
</select>
		
<select id="selectAllUsers" resultType="com.atguigu.ibatis.bean.User">
	select * from users
</select>

2). 在config.xml中注册这个映射文件  

<mapper resource=" com/atguigu/ibatis/bean/userMapper.xml"/>

 3). 在dao中调用：

public User getUserById(int id) {
	SqlSession session = sessionFactory.openSession();
	User user = session.selectOne(URI+".selectUser", id);
	return user;
}

 3.2. 注解的实现

 1). 定义sql映射的接口

public interface UserMapper {
	@Insert("insert into users(name, age) values(#{name}, #{age})")
	public int insertUser(User user);

	@Delete("delete from users where id=#{id}")
	public int deleteUserById(int id);
			
	@Update("update users set name=#{name},age=#{age} where id=#{id}")
	public int updateUser(User user);

	@Select("select * from users where id=#{id}")
	public User getUserById(int id);

	@Select("select * from users")
	public List<User> getAllUser();
}

 2). 在config中注册这个映射接口

<mapper class="com.atguigu.ibatis.crud.ano.UserMapper"/>

       3) . 在dao类中调用

public User getUserById(int id) {
	SqlSession session = sessionFactory.openSession();
	UserMapper mapper = session.getMapper(UserMapper.class);
	User user = mapper.getUserById(id);
	return user;
}

 4. 几个可以优化的地方

4.1. 连接数据库的配置单独放在一个properties文件中

## db.properties

<properties resource="db.properties"/>

<property name="driver" value="${driver}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password}" />

4.2. 为实体类定义别名,简化sql映射xml文件中的引用

<typeAliases>
	<typeAlias type="com.atguigu.ibatis.bean.User" alias="_User"/>
</typeAliases>

  4.3. 可以在src下加入log4j的配置文件,打印日志信息

 5. 解决字段名与实体类属性名不相同的冲突

5.1. 准备表和数据：

CREATE TABLE orders(
	order_id INT PRIMARY KEY AUTO_INCREMENT,
	order_no VARCHAR(20), 
	order_price FLOAT
);
INSERT INTO orders(order_no, order_price) VALUES('aaaa', 23);
INSERT INTO orders(order_no, order_price) VALUES('bbbb', 33);
INSERT INTO orders(order_no, order_price) VALUES('cccc', 22);

5.2. 定义实体类：

public class Order {
	private int id;
	private String orderNo;
	private float price;
}

5.3. 实现getOrderById(id)的查询：