Mybatis多表查询
一、简介
MyBatis 是一款优秀的 ORM 框架，支持多表查询操作。在实际开发中，经常需要使用多表查询来获取业务数据。
表与表之间存在的三种关系：一对一，一对多，多对多
二、一对一
1.pojo
student（学生类）
import java.util.List;
public class Student {
private int id;
private String studentName;
private String gender;
private String address;
private String email;
private String remark;
public Student() {
}
public Student(String studentName, String gender, String address,String remark) {
this.studentName = studentName;
this.gender = gender;
this.address = address;
this.remark = remark;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getRemark() {
return remark;
}
public void setRemark(String remark) {
this.remark = remark;
}
}order（订单类）
import java.util.List;
public class Order {
private int id;
private String ordername;
private int ordercount;
private Student student;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getOrdername() {
return ordername;
}
public void setOrdername(String ordername) {
this.ordername = ordername;
}
public int getOrdercount() {
return ordercount;
}
public void setOrdercount(int ordercount) {
this.ordercount = ordercount;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
}2.queryOrder接口类
public interface QueryOrderMapper {
public List findOrderStudentAll();
} 3.OrderMapper.xml
4.test测试
@Test
public void testMapper6(){
SqlSession sqlSession = ssf.openSession();
QueryOrderMapper mapper = sqlSession.getMapper(QueryOrderMapper.class);
List orders = mapper.findOrderStudentAll();
QueryOrderStudent student = new QueryOrderStudent();
for (Order order : orders) {
System.out.println(
order.getOrdername()+","+order.getOrdercount()+","+
student.getId()+","+student.getStudentName()
+","+student.getAddress()
);
}
} 三、一对多
1.pojo
student.java
package com.batis.domain;
import java.util.List;
public class Student {
private int id;
private String studentName;
private String gender;
private String address;
private String email;
private String remark;
private List listOrder;
public Student() {
}
public Student(String studentName, String gender, String address,String remark) {
this.studentName = studentName;
this.gender = gender;
this.address = address;
this.remark = remark;
}
public List getListOrder() {
return listOrder;
}
public void setListOrder(List listOrder) {
this.listOrder = listOrder;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public String getGender() {
return gender;
}
public void setGender(String gender) {
this.gender = gender;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getRemark() {
return remark;
}
public void setRemark(String remark) {
this.remark = remark;
}
}
order.java
import java.util.List;
public class Order {
private int id;
private String ordername;
private int ordercount;
private Student student;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getOrdername() {
return ordername;
}
public void setOrdername(String ordername) {
this.ordername = ordername;
}
public int getOrdercount() {
return ordercount;
}
public void setOrdercount(int ordercount) {
this.ordercount = ordercount;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
}2.StudentMapper接口类
public interface StudentMapper {
public List findStudentOrderAll();
} 3.StudentMapper.xml
4.test测试
@Test
public void testMapper8(){
SqlSession sqlSession = ssf.openSession();
StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
List students = mapper.findStudentOrderAll();
for (Student student : students) {
System.out.println(student.getId()+","+student.getStudentName()+","+student.getAddress());
List listOrder = student.getListOrder();
for (Order order : listOrder) {
System.out.println(order.getOrdername()+","+order.getOrdercount());
}
}
} 四、多对多
1.pojo
items（物品类）
public class Items {
private int id;
private String items_name;
private int items_price;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getItems_name() {
return items_name;
}
public void setItems_name(String items_name) {
this.items_name = items_name;
}
public int getItems_price() {
return items_price;
}
public void setItems_price(int items_price) {
this.items_price = items_price;
}
}
order
import java.util.List;
public class Order {
private int id;
private String ordername;
private int ordercount;
private Student student;
private List orderDetailList;
public List getOrderDetailList() {
return orderDetailList;
}
public void setOrderDetailList(List orderDetailList) {
this.orderDetailList = orderDetailList;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getOrdername() {
return ordername;
}
public void setOrdername(String ordername) {
this.ordername = ordername;
}
public int getOrdercount() {
return ordercount;
}
public void setOrdercount(int ordercount) {
this.ordercount = ordercount;
}
public Student getStudent() {
return student;
}
public void setStudent(Student student) {
this.student = student;
}
} orderdetail（订单详细）
import java.util.List;
public class OrderDetail {
private int id;
private int item_count;
private int item_all_price;
private Order orderL;
private List itemsList;
public Order getOrderL() {
return orderL;
}
public void setOrderL(Order orderL) {
this.orderL = orderL;
}
public List getItemsList() {
return itemsList;
}
public void setItemsList(List itemsList) {
this.itemsList = itemsList;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public int getItem_count() {
return item_count;
}
public void setItem_count(int item_count) {
this.item_count = item_count;
}
public int getItem_all_price() {
return item_all_price;
}
public void setItem_all_price(int item_all_price) {
this.item_all_price = item_all_price;
}
}
2.queryOrder接口类
import com.batis.domain.Order;
import java.util.List;
public interface QueryOrderMapper {
public List findOrderStudentItemsOrderDetail();
} 3.OrderMapper.xml
4.test测试
@Test
public void testMapper9(){
SqlSession sqlSession = ssf.openSession();
QueryOrderMapper mapper = sqlSession.getMapper(QueryOrderMapper.class);
List orders = mapper.findOrderStudentItemsOrderDetail();
for (Order order : orders) {
System.out.println(order.getId()+","+order.getOrdername()+","+order.getStudent().getStudentName()+","+order.getStudent().getGender());
List orderDetailList = order.getOrderDetailList();
for (OrderDetail orderDetail : orderDetailList) {
System.out.println(orderDetail.getId()+","+orderDetail.getItem_count()+","+orderDetail.getItem_all_price());
List itemsList = orderDetail.getItemsList();
for (Items items : itemsList) {
System.out.println(items.getItems_name()+","+items.getItems_price());
}
}
}
}