知識點：查詢一個實體類，並查出這個類下面的集合

Employee.java實體類

package com.hand.mybatis.bean;
public class Employee {
private Integer eId;
private String eName;
private Integer gender;
private String email;
private Department dept;

public Employee() {
super();
}
public Employee(Integer eId,String eName, Integer gender, String email) {
super();
this.eId=eId;
this.eName = eName;
this.gender = gender;
this.email = email;
}


public Integer geteId() {
return eId;
}
public void seteId(Integer eId) {
this.eId = eId;
}

public String getEName() {
return eName;
}
public void setEname(String ename) {
this.eName = ename;
}
public Integer getGender() {
return gender;
}
public void setGender(Integer gender) {
this.gender = gender;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public Department getDept() {
return dept;
}
public void setDept(Department dept) {
this.dept = dept;
}
@Override
public String toString() {
return "Employee [eId=" + eId + ", ename=" + eName + ", gender=" + gender + ", email=" + email + "]";
}

}

Department.java實體類

package com.hand.mybatis.bean;
import java.util.List;

public class Department {
private Integer id;
private String departName;
private List<Employee> empList;

public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getDepartName() {
return departName;
}
public void setDepartName(String departName) {
this.departName = departName;
}

public List<Employee> getEmpList() {
return empList;
}
public void setEmpList(List<Employee> empList) {
this.empList = empList;
}

@Override
public String toString() {
return "Department [id=" + id + ", departName=" + departName + "]";
}

}

DepartmentMapper.java接口

package com.hand.mybatis.dao;
import com.hand.mybatis.bean.Department;

public interface DepartmentMapper {

Department getDeptById(Integer did);

//根據部門id，查詢部門信息，同時將部門下的所有員工信息查詢出來
Department getDeptByIdPlus(Integer did);

//分步查詢部門信息
Department getDeptByIdStep(Integer did);
}

DepartmentMapper.xm l映射文件

<?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.hand.mybatis.dao.DepartmentMapper">

<!-- Department getDeptById(Integer did); -->
<select id="getDeptById" resultType="com.hand.mybatis.bean.Department">
SELECT did id,deptname departName FROM dept WHERE did=#{did}
</select>

<!--1.查詢部門的時候將部門對應的所有員工信息也查詢出來
-->

<resultMap type="com.hand.mybatis.bean.Department" id="departmentMap">
<result property="id" column="did"/>
<result property="departName" column="deptname"/>
<!--collection定義關聯集合類型的屬性的封裝規則
ofType:指定集合裏面元素的類型 -->
<collection property="empList" ofType="com.hand.mybatis.bean.Employee">
<!-- 定義這個集合元素的封裝規則 -->
<id column="eid" property="eId"/>
<result column="ename" property="eName"/>
<result column="email" property="email"/>
<result column="gender" property="gender"/>
</collection>
</resultMap>

<!-- Department getDeptByIdStep(Integer did); --> 接口一：根據部門did查詢部門信息，員工信息
<select id="getDeptByIdPlus" resultMap="departmentMap">
SELECT d.did,d.deptname,e.eid,e.ename,e.email,e.gender
FROM dept d
LEFT JOIN emp e
ON d.did=e.did
WHERE d.did=#{did}
</select>


<!--2. select_resultMap關聯查詢collection分步查詢 -->

<resultMap type="com.hand.mybatis.bean.Department" id="departmentMapPlus">
<id column="did" property="id"/>
<result column="deptname" property="departName"/>
<collection property="empList"
select="com.hand.mybatis.dao.EmployeeMapper.getEmpByDeptId"
column="{dId=did}" fetchType="lazy">//可以多列傳值
</collection>
</resultMap>

<!--Department getDeptByIdStep(Integer did); -->接口二：根據部門id分步查詢員工信息
<select id="getDeptByIdStep" resultMap="departmentMapPlus">
SELECT did,deptname
from dept
WHERE did=#{did}
</select>

<!-- 擴展，多列的值傳遞過去，將多列的值封裝map傳遞
column="{key1=column1,key2=column2}"
fetchType="lazy":表示使用延遲加載
- lazy:延遲
- eager:立即-->

</mapper>

mybatis映射文件select_resultMap_關聯查詢_collection定義關聯集合