Mybatis

0.需要导入的包

1.先创建Mapper接口

再写入要实现的方法,再创建Mapper.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!-- 对象的映射关系 -->
<mapper namespace="Mapper接口的全限定名">
    <resultMap id="dapt_Mapping" type="Department类的全限定名">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
    </resultMap>

    <insert id="add" keyColumn="id" keyProperty="id" useGeneratedKeys="true" >
        insert into dept(name) value (#{name})
    </insert>

    <select id="get" resultMap="dapt_Mapping" >
        select id, name from dept where id=#{id}
    </select>

</mapper>

2. 创建一个 xxx.cfg.xml文件

<?xml version="1.0" encoding="UTF-8" ?>
<!-- 针对没有把提示框架的配置 -->
<configuration>
    <properties resource="db.properties" />
    <!-- 对Mybatis的运行状态进行配置 -->
    <settings>
        <!-- 开启延迟加载
            全局启用或禁用延迟加载。当禁用时, 所有关联对象都会即时加载
        -->
        <setting name="lazyLoadingEnabled" value="true"/>
        <!-- 当启用时, 有延迟加载属性的对象在被调用时将会完全加载任意属性.否则, 每种属性将会按需要加载,默认是开启的 -->
        <setting name="aggressiveLazyLoading" value="false"/>
        <!-- Object对象上面的哪些方法触发延迟加载. 一般只写clone -->
        <setting name="lazyLoadTriggerMethods" value="clone"/>
    </settings>
    <!-- 使用typeAliases为类型取别名 -->
    <typeAliases>

　　　　<typeAlias type="domain的全限定名" alias="User" />
　　　　<typeAlias type="domain的全限定名" alias="Employee" />
　　　　<typeAlias type="domain的全限定名" alias="Department" />

    </typeAliases>
    <!-- 环境 -->
    <environments default="default">
        <environment id="default">
            <!-- 配置事务管理器 -->
            <transactionManager type="JDBC" />
            <!-- 数据库连接池 -->
            <dataSource type="POOLED" >
                <property name="driver" value="${driverClassName}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>
    <!-- 告诉Mybatis要管理mapper文件 -->
    <mappers>
　　　　<mapper resource="Mapper.xml的全限定名" />
    </mappers>
</configuration>

3. many2one

<?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">
<!-- 对象的映射关系 -->
<mapper namespace="Mapper接口的全限定名">

    <resultMap id="emp_Mapping" type="domain的全限定名">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <!-- 关联的映射 : 使用额外的SQL关联数据库属性 -->
        <association property="dept" javaType="Department" column="dept_id"
                     select="Mapper接口的全限定名.get"/>
    </resultMap>
    
    <!-- 内联关联 -->
    <resultMap id="list_mapping" type="domain的全限定名">
        <id column="id" property="id"/>
        <result column="name" property="name"/>

        <!-- 使用内联的方式映射 -->
        <association property="dept" javaType="Department" >
            <id column="did" property="id" />
            <result column="dname" property="name" />
        </association>
    </resultMap>
    

    <insert id="add" keyColumn="id" keyProperty="id" useGeneratedKeys="true">
        inset into employee(name, dept_id) value (#{name}, #{dept.id})
    </insert>
　　// resultMap: 返回的是自己在resultMap中定义的
    <select id="get" resultMap="emp_Mapping">
        select id, name, dept_id from employee where id=#{id}
    </select>

    <select id="list" resultMap="list_mapping">
        select e.id, e.name, d.id as did, d.name as dname
        from employee e left join dept d on e.dept_id = d.id
    </select>
　　// resultType: 返回的是在domain中定义的
    <select id="autoComplateList" resultType="domain的全限定名" >
        select id,name from employee
    </select>
</mapper>

4. 测试

import org.junit.Test;

import java.util.List;

public class Many2OneTest {
    @Test
    public void testSave() {
        Department d = new Department();
        d.setName("d");
        Employee e = new Employee();
        e.setName("e");
        e.setDept(d);
        SqlSession session = MybatisUtil.openSession();
　　　　　// session.getMapper是获取Department的字节码
        DepartmentMapper dmapper = session.getMapper(DepartmentMapper.class);
        EmployeeMapper emapper = session.getMapper(EmployeeMapper.class);
        dmapper.add(d);
        emapper.add(e);
　　　　 // 提交事务
        session.commit();
　　　　 // 关闭资源
        session.close();
    }

    @Test
    public void testGet() {
        SqlSession session = MybatisUtil.openSession();
        DepartmentMapper dmapper = session.getMapper(DepartmentMapper.class);
        EmployeeMapper emapper = session.getMapper(EmployeeMapper.class);
        Employee e = emapper.get(7L);
        Department d = e.getDept();
        System.out.println(e);
        System.out.println(d);
        session.close();
    }
    @Test
    public void testCache() {
        SqlSession session = MybatisUtil.openSession();
        EmployeeMapper emapper = session.getMapper(EmployeeMapper.class);
        emapper.get(7L);
        session.clearCache();
        emapper.get(7L);
        session.close();

    }

    @Test
    public void testList() {
        SqlSession session = MybatisUtil.openSession();
        EmployeeMapper emapper = session.getMapper(EmployeeMapper.class);
        List<Employee> es = emapper.list();
        for (Employee e : es) {
            System.out.println(e.getName() + "        " + e.getDept().getId());
        }
        session.close();
    }

    @Test
    public void testAutoList() {
        SqlSession session = MybatisUtil.openSession();
        EmployeeMapper emapper = session.getMapper(EmployeeMapper.class);
        List<Employee> es = emapper.autoComplateList();
        System.out.println(es);
        session.close();

    }

}

5. MyUtil

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 java.io.IOException;

public class MybatisUtil {
    private static MybatisUtil instance = new MybatisUtil();
    private SqlSessionFactory factory;

    private MybatisUtil() {
        try {
            factory = new SqlSessionFactoryBuilder()
                    .build(Resources.getResourceAsReader("mybatis.cfg.xml"));
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession openSession() {
        return instance.factory.openSession();
    }

    public static <T> T getMapper(Class<T> tClass) {
        SqlSession session = openSession();
        T mapper = session.getMapper(tClass);
        return mapper;
    }

}