MyBatis的級聯查詢（兩種方式）
https://blog.csdn.net/zhupengqq/article/details/78575767
與上次唯一不同的一下幾個類
Department.java
package com.cn.zhu.bean;
public class Department {
private Integer id;
private String departmentName;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getDepartmentName() {
return departmentName;
}
public void setDepartmentName(String departmentName) {
this.departmentName = departmentName;
}
@Override
public String toString() {
return "Department [departmentName=" + departmentName + ", id=" + id
+ "]";
}
}
Employee.java
package com.cn.zhu.bean;
import org.apache.ibatis.type.Alias;
@Alias("emp")
public class Employee {
private Integer id;
private String lastName;
private String email;
private String gender;
private Department dept;
public Employee() {
super();
// TODO Auto-generated constructor stub
}
public Employee(Integer id, String lastName, String email, String gender) {
super();
this.id = id;
this.lastName = lastName;
this.email = email;
this.gender = gender;
}
public Department getDept() {
return dept;
}
public void setDept(Department dept) {
this.dept = dept;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
@Override
public String toString() {
return "Employee [email=" + email + ", gender=" + gender + ", id=" + id
+ ", lastName=" + lastName + "]";
}
}
EmployeeMapperPlus.java
package com.cn.mybatis.dao;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.annotations.MapKey;
import org.apache.ibatis.annotations.Param;
import com.cn.zhu.bean.Employee;
public interface EmployeeMapperPlus {
public Employee getEmpById(Integer id);
public Employee getEmpAndDept(Integer id);
}
EmployeeMapperPlus.xml
<?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="com.cn.mybatis.dao.EmployeeMapperPlus">
<!--
自定義某個javaBean的封裝規則 id 定義主鍵會底層有優化 type: 自定義規則的java型別 property :
唯一id方便引用
-->
<!--
<resultMap type="com.cn.zhu.bean.Employee" id="MySimpleEmp"> 指定主鍵的封裝規則
column 指定哪一列 property 指定對應的javaBean屬性 <id column="id" property="id"/>
定義普通列封裝 <result column="last_name" property="lastName"/> 其他不指定的列會自動封裝
，我們只要寫resultMap就把全部的對映規則都寫上 <result column="email" property="email"/>
<result column="gender" property="gender"/> </resultMap>
--><!-- public Employee getEmpById(Integer id); -->
<!-- resultMap: 自定義結果集對映規則 -->
<!--
<select id="getEmpById" resultMap="MyEmp"> select * from tal_employee
where id=#{id} </select>
-->
<!--
場景一 ： 查詢Employee的同時查詢員工對應的部門 Employee ===department 一個員工有與之對應的部門資訊
-->
<resultMap type="com.cn.zhu.bean.Employee" id="MyDifEmp">
<!--
指定主鍵的封裝規則 column 指定哪一列 property 指定對應的javaBean屬性
-->
<!--
聯合查詢 ：級聯屬性封裝結果
-->
<id column="id" property="id" />
<!-- 定義普通列封裝 -->
<result column="last_name" property="lastName" />
<!-- 其他不指定的列會自動封裝 ，我們只要寫resultMap就把全部的對映規則都寫上 -->
<result column="gender" property="gender" />
<result column="did" property="dept.id" />
<result column="dept_name" property="dept.departmentName" />
</resultMap>
<!-- 使用association 定義單個物件的封裝規則 -->
<resultMap type="com.cn.zhu.bean.Employee" id="MyDifEmp2">
<id column="id" property="id" />
<!-- 定義普通列封裝 -->
<result column="last_name" property="lastName" />
<!-- 其他不指定的列會自動封裝 ，我們只要寫resultMap就把全部的對映規則都寫上 -->
<result column="gender" property="gender" />
<!--association 可以指定聯合的javaBean物件
property 指定哪個是聯合的物件
javaType: 指定這個屬性物件的型別
-->
<association property="dept" javaType="com.cn.zhu.bean.Department">
<id column="did" property="id"/>
<result column="dept_name" property="departmentName"/>
</association>
</resultMap>
<!-- public Employee getEmpAndDept(Integer id); -->
<select id="getEmpAndDept" resultMap="MyDifEmp2">
SELECT e.id id,e.last_name last_name ,e.gender gender,e.d_id d_id,
d.id did,d.dept_name dept_name from tbl_employee e,tbl_dept d
where e.d_id=d.id and e.id=#{id}
</select>
</mapper>
以上是兩種對映封裝結果
增加EmployeeMapperPlus.xml 後，一定要在mybatis-config.xml里加上這個配置檔案的宣告，
<mappers>
<mapper resource="mybatis/mapper/EmployeeMapperPlus.xml" />
</mappers>
另外sql語句一定要正確，可以先在navict資料庫圖形化管理工具中，測試sql
下面編寫測試類（這裡直接寫測試方法吧）：詳細請看對映一
@Test
public void test05() throws IOException{
SqlSessionFactory sqlsessionFactory=getSqlSessionFactory();
// 1 獲取到的sqlsession不會自動提交資料
SqlSession openSession=sqlsessionFactory.openSession();
try{
EmployeeMapperPlus mapper=openSession.getMapper(EmployeeMapperPlus.class);
Employee empAndDept=mapper.getEmpAndDept(1);
System.out.println(empAndDept);
System.out.println(empAndDept.getDept());
}finally{
openSession.commit();
}
}
測試完成