Mybatis中使用Collection元素进行一对多级联查询

来源：互联网发布：知乎花儿郭阳编辑：程序博客网时间：2024/06/10 04:16

Collection主要处理“一对多”类型映射关系，例如，查询部门中有多个员工，就需要使用的到集合：List<employee> emp,这样，就会使用collection进行映射关联查询。

1.employee.java

package com.casv.model;public class employee {private int uid;private String name;private String pwd;private department dept;public int getUid() {return uid;}public void setUid(int uid) {this.uid = uid;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPwd() {return pwd;}public void setPwd(String pwd) {this.pwd = pwd;}public department getDept() {return dept;}public void setDept(department dept) {this.dept = dept;}}

2.department.java

package com.casv.model;import java.util.List;public class department {   private int pid;private String pname;//使用List集合保存员工信息，并关联employee实体类    private List<employee> emplist;public int getPid() {return pid;}public void setPid(int pid) {this.pid = pid;}public String getPname() {return pname;}public void setPname(String pname) {this.pname = pname;}public List<employee> getEmplist() {return emplist;}public void setEmplist(List<employee> emplist) {this.emplist = emplist;}}

3.deptMapper.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mapper SYSTEM "http://mybatis.org/dtd/mybatis-3-mapper.dtd" ><mapper namespace="com.casv.dao.deptMapper">    <resultMap id="departResulMap" type="depts" >       <id column="p_id" property="pid"/>       <result column="p_name" property="pname"/>       <!-- 使用collection将employee实体类中字段属性嵌套进来 -->       <collection column="p_id" property="emplist" ofType="emps" >           <id column="u_id" property="uid"></id>   <result column="u_name" property="name"></result>    <result column="u_pwd" property="pwd"></result>       </collection>    </resultMap>    <select id="selectDeptFetchEmp" parameterType="int" resultMap="departResulMap">        <!-- 查询根据部门id查询有那些员工在其部门 -->        select * from t_dept d inner join t_user u where d.p_id=u.p_id and d.p_id=#{id}    </select></mapper>

ofType属性可以区分是JavaBean（或字段）属性，还是集合包含属性，读作：“在emps对象类型中ArrayList中的emplist集合”。

4.config.xml中注册deptMapper.xml

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE configuration SYSTEM "http://mybatis.org/dtd/mybatis-3-config.dtd" ><configuration><!-- 配置实体类，起别名 --><typeAliases><typeAlias type="com.casv.model.employee" alias="emps" /><typeAlias type="com.casv.model.department" alias="depts"/><!-- 扫描实体类包，后续可以直接使用类名<package name="com.casv.model.User"/>--></typeAliases><!-- 配置数据源 --><environments default="development"><environment id="development"><transactionManager type="JDBC"></transactionManager><dataSource type="POOLED"><property name="driver" value="com.mysql.jdbc.Driver" /><property name="url" value="jdbc:mysql://localhost:3306/userdatabase" /><property name="username" value="root" /><property name="password" value="123456" /></dataSource></environment></environments><mappers><!-- 注册deptMapper.xml --><mapper resource="com/casv/dao/deptMapper.xml"></mapper></mappers></configuration>

5.编写test测试类

@Test public void test2(){    session=MyBatisUtil.getSessionFactory().openSession();    department dept=session.selectOne("com.casv.dao.deptMapper.selectDeptFetchEmp", 1);    for(employee emp : dept.getEmplist()){System.out.println(emp.getName()+" "+dept.getPname());    }    session.close();}

0 0