mybatis总结（三）之多表查询

上一节，已经把实体类和配置文件都写过了，这节课直接添加几个方法吧

在DeptMapper.xml文件中添加

<!-- 多表查询(1对多) ,通过部门编号，查询出部门所在的员工姓名，部门名，部门编号 -->
	<select id="selectByDeptno" resultMap="deptResult">
		select
		ename,dept.deptno,dname
		from dept join emp
		on dept.deptno=emp.deptno
		where dept.deptno=#{deptno}
	</select>
	<!-- one 方 -->
	<resultMap type="Dept" id="deptResult">
		<!-- id指定主键的相关信息（列名、属性名） -->
		<id property="deptno" column="deptno" />
		<!-- result定义除了主键列之外的其他字段 -->
		<result property="dname" column="dname" />
		<collection property="emps" ofType="Emp" resultMap="empResult"
			foreignColumn="deptno" />
	</resultMap>
	<!-- many方 -->
	<resultMap id="empResult" type="Emp">
		<id property="empno" column="empno" />
		<result property="ename" column="ename" />
	</resultMap>

	<!--一对一查询  -->
	<!-- 通过员工编号，查询该员工姓名、所在部门名称 -->
	<select id="selectByEmpno" resultMap="empResult1">
		select
		ename,dept.deptno,dname
		from
		emp join dept
		on emp.deptno=dept.deptno
		where emp.empno=#{empno}
	</select>
	<resultMap id="empResult1" type="Emp">
		<id property="empno" column="empno" />
		<result property="ename" column="ename" />
		<association property="dept" javaType="Dept"
			foreignColumn="deptno" resultMap="deptResult1"></association>
	</resultMap>
	<resultMap id="deptResult1" type="Dept">
		<!-- id指定主键的相关信息（列名、属性名） -->
		<id property="deptno" column="deptno" />
		<!-- result定义除了主键列之外的其他字段 -->
		<result property="dname" column="dname" />
	</resultMap>

2. mapper接口

public interface DeptMapper {
	public Dept selectByDeptno(int deptno);
	public Emp selectByEmpno(int empno);
}

3.测试方法

public class DeptTest {
	public static void main(String[] args) throws IOException {
		// 指定mybatis配置文件路径和文件名
		String resource = "mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder()
				.build(inputStream);
		SqlSession session = sqlSessionFactory.openSession();
		try {
			// session.selectOne(配置文件中namespace.id,传入参数的值)
			//通过接口，调用方法（接口名和namespace名称保持一致，id和方法名保持一致）
			DeptMapper mapper = session.getMapper(DeptMapper.class);

			//一对多查询
			Dept dept=mapper.selectByDeptno(10);
			System.out.println(dept.getDeptno()+dept.getLoc()+dept.getDname());
			List<Emp> list=dept.getEmps();
			for (Emp emp : list) {
				System.out.println(emp.getEname());
			}
			//一对一查询
			Emp emp=mapper.selectByEmpno(7499);
			System.out.println("部门编号："+emp.getDept().getDeptno()+"部门名字:"+emp.getDept().getDname()+"员工名字:"+emp.getEname());
			}
		} finally {
			session.close();
		}

	}
}