mybatis__关联关系__1对1，1对多

这里有两张Emp数据表、Dept数据表

雇员表：Emp(empno,ename,job,deptno)

部门表：Dept(deptno,dname,loc)

一个雇员对应着一个部门，是1对1的关系；
而反过来看，一个部门对应着多个雇员，是1对多的关系；

association: 一对一关联(has one)
collection:一对多关联(has many)

1对1的关系

一个雇员对应着一个部门，是1对1的关系；
一个Emp对象里有一个Dept对象

Pojo类

Emp

package com.zsl.pojo;
import java.util.List;
public class Emp {
	private Integer empno;
	private String ename;
	private String job;
	
	private Dept dept;
	
	public Integer getEmpno() {
		return empno;
	}
	public void setEmpno(Integer empno) {
		this.empno = empno;
	}
	public String getEname() {
		return ename;
	}
	public void setEname(String ename) {
		this.ename = ename;
	}
	public String getJob() {
		return job;
	}
	public void setJob(String job) {
		this.job = job;
	}

	public Emp() {
		super();
		// TODO Auto-generated constructor stub
	}
	public Dept getDept() {
		return dept;
	}
	public void setDept(Dept dept) {
		this.dept = dept;
	}
	public Emp(Integer empno, String ename, String job) {
		super();
		this.empno = empno;
		this.ename = ename;
		this.job = job;
	}
	@Override
	public String toString() {
		return "Emp [empno=" + empno + ", ename=" + ename + ", job=" + job + "]";
	}
}

EmpMapper接口

public interface EmpMapper {
	public List<Emp> queryE();
}

EmpMapper.xml映射文件

<resultMap type="emp" id="baseMap">
		<!-- 主表数据 -->
		<id column="empno" property="empno"/>
		<result column="ename" property="ename"/>
		<result column="job" property="job"/>
		
<!--1对1的关系, property: 指的是Emp对象的属性值（定义从表的变量名，Dept对象为Emp属性之一）, javaType：指的是属性的类型,这里使用了别名 -->	
		<association property="dept" javaType="dept">
<!--从表数据 -->
<!—-column：数据表字段名，property：属性值 -->
			<id column="deptno" property="deptno"/>
			<result column="dname" property="dname"/>
			<result column="loc" property="loc"/>
		</association>
	</resultMap>
	
	<select id="queryE" resultMap="baseMap">
		select
			t1.empno
			,t1.ename
			,t1.job
			,t2.deptno
			,t2.dname
			,t2.loc 
		from emp t1
			left join dept t2
			on t1.deptno = t2.deptno
	</select>

1对多关系

查询出所有的部门信息及该部门下所有员工的信息
一个部门对应着多个雇员，是1对多的关系；
一个Dept对象里有一个Emp的集合

pojo类

Dept

package com.zsl.pojo;
import java.util.List;
public class Dept {
	
	private Integer deptno;
	private String dname;
	private String loc;
	
	private List<Emp> emps;

	public Integer getDeptno() {
		return deptno;
	}

	public void setDeptno(Integer deptno) {
		this.deptno = deptno;
	}

	public String getDname() {
		return dname;
	}

	public void setDname(String dname) {
		this.dname = dname;
	}

	public String getLoc() {
		return loc;
	}

	public void setLoc(String loc) {
		this.loc = loc;
	}

	public List<Emp> getEmps() {
		return emps;
	}

	public void setEmps(List<Emp> emps) {
		this.emps = emps;
	}

	public Dept() {
		super();
		// TODO Auto-generated constructor stub
	}

	public Dept(Integer deptno, String dname, String loc) {
		super();
		this.deptno = deptno;
		this.dname = dname;
		this.loc = loc;
	}

	@Override
	public String toString() {
		return "Dept [deptno=" + deptno + ", dname=" + dname + ", loc=" + loc + "]";
	}
}

DeptMapper接口

public interface DeptMapper {
	public List<Dept> queryD();
}

DeptMapper.xml映射文件

<resultMap type="dept" id="baseMap">
			<!-- 主表数据 -->
  			<id column="deptno" property="deptno"/>
  			<result column="dname" property="dname"/>
  			<result column="loc" property="loc"/>
  			
  			<!-- 1 对 多的关联关系通过 collection配置
  				property 对应的就是对象中的多的那方的变量名称
  				ofType:就是集合中的泛型的类型 -->
  			
  			<!-- 从表数据 -->
<!-- column：数据表字段名，property：属性值-->
  			<collection property="emps" ofType="emp">
  				<id column="empno" property="empno"/>
  				<result column="ename" property="ename"/>
  				<result column="job" property="job"/>
  			</collection>
  		</resultMap>
  		
  		<select id="queryD" resultMap="baseMap">
  			select
  				t1.deptno
  			    ,t1.dname
  			    ,t1.loc
  			    ,t2.empno
  			    ,t2.ename
  			    ,t2.job		
  			from dept t1
  			   left join emp t2
  			      on t1.deptno = t2.deptno
  		</select>

全局配置文件

mybatis-cfg.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>
 <!-- 导入外部资源 -->
 <properties resource="db.properties"/>

	<!-- <settings> 开启延迟加载
		<setting name="lazyLoadingEnabled" value="true" />
		<setting name="aggressiveLazyLoading" value="false" />
	</settings> -->

  <!-- 自定义别名 -->
    <typeAliases>
        <typeAlias type="com.zsl.pojo.Emp" alias="emp"/>
        <typeAlias type="com.zsl.pojo.Dept" alias="dept"/>
    </typeAliases>
    
    
 <!-- 环境 -->
  <environments default="development">
    <environment id="development">
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${driver}"/>
        <property name="url" value="${url}"/>
        <property name="username" value="${userName}"/>
        <property name="password" value="${password}"/>
      </dataSource>
    </environment>
  </environments>
  
  <!-- 注册映射文件 -->
  <mappers>
  	<mapper resource="EmpMapper.xml"/>
  	<mapper resource="DeptMapper.xml"/>
  	<!-- <package name="包名"/> -->
  </mappers>
</configuration>
  

DBUtils

package com.zsl.utils;

import java.io.IOException;
import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

public class DbUtils {
	public static SqlSession getSession() throws IOException {
		// TODO Auto-generated method stub
		// 1.通过Resources对象加载配置文件
		InputStream inputStream = Resources.getResourceAsStream("mybatis-cfg.xml");
		// 2.获取SqlSessionFactory对象
		SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(inputStream);
		// 3.通过SqlSessionFactory对象获取SQLSession对象
		SqlSession session = factory.openSession();
		return session;
	}
	
	public static void commit(SqlSession session) {
		// TODO Auto-generated method stub
		session.commit();
	}
	
	public static void close(SqlSession session) {
		// TODO Auto-generated method stub
		session.close();
	}
}

测试类Test

package com.zsl.test;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

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 com.zsl.dao.DeptMapper;
import com.zsl.dao.EmpMapper;
import com.zsl.pojo.Dept;
import com.zsl.pojo.Emp;
import com.zsl.utils.DbUtils;

public class Test {
	public static void main(String[] args) throws IOException {

		Test test = new Test();
		System.out.println(test.queryD());
	}
	
	public List<Emp> queryE() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		EmpMapper mapper = session.getMapper(EmpMapper.class);
		List<Emp> list = mapper.queryE();
		session.close();
		return list;
	}

	public List<Dept> queryD() throws IOException {
		// TODO Auto-generated method stub
		SqlSession session = DbUtils.getSession();
		DeptMapper mapper = session.getMapper(DeptMapper.class);
		List<Dept> list = mapper.queryD();
		session.close();
		return list;
	}

}

多对多关系

双向的1对多既是多对多关系
就是两个对象互相以集合的形式为对方的属性
然后两个映射文件里配置resultMap 使用collection