初识MyBatis

Posted 2020-09-27

Mybatis
1.持久化
持久化，就是内存数据和硬盘数据状态的转换
2.ORM思想
Object Relation Mapping 对象关系映射
3.MyBatis入门案例
3.1导入jar包
依赖
<!--mysql配置-->
<dependency>
<groupId>MySQL</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.0.8</version>
</dependency>
<!--MyBatis核心jar包-->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.2.2</version>
</dependency>

3.2书写大配置

<?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/y2165"/>
<property name="username" value="root"/>
<property name="password" value="root"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="org/mybatis/example/BlogMapper.xml"/>
</mappers>
</configuration>
3.3实体类
public class StudentInfo {
private Integer stuId;
private String stuName;
private Integer stuAge;
private Date stuDate;
}

3.4小配置
<?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="cn.happy.dao.IStudentInfoDAO">
<select id="findAll" resultType="cn.happy.entity.StudentInfo">
select * from studentinfo
</select>
</mapper>

两个注意事项：
1.你得更新POM.xml文件中build节点
<build>
<resources>
<resource>
<directory>src/main/java</directory>
<includes>
<include>**/*.xml</include>
</includes>
</resource>
</resources>
</build>

2.你得在大配置中关联小配置文件
<mappers>
<mapper resource="cn/happy/dao/IStudentInfoDAO.xml"/>
</mappers>

3.5 写测试类
3.5.1 String path="大配置的路径名";
InputStream is=Resources.getResourcesAsStream(path);
SessionFactory factory=new SessionFactoryBuilder().build(is);
SqlSession session=factory.openSession();

结论：
1. 注意小配置的命名空间的名称

4.别名的使用
<typeAliases>
<!--<typeAlias type="cn.happy.entity.StudentInfo" alias="StudentInfo"></typeAlias>-->
<!--将该包中的简单类型 StudentInfo作为类的别名-->
<package name="cn.happy.entity"></package>
</typeAliases>

5.getMapper() 动态代理数据
class<T> 类型的类型
is = Resources.getResourceAsStream(path);
SqlSessionFactory factory=new SqlSessionFactoryBuilder().build(is);
SqlSession session=factory.openSession();
IStudentInfoDAO dao = session.getMapper(IStudentInfoDAO.class);
StudentInfo info = dao.getStudentById(3);
System.out.println(info.getStuName());