day03-2-拓展

乎语百科 2022-10-22 00:26:06 210 0

满汉楼03

5.拓展_多表查询

前面都是对单表进行操作

思考一个问题：如果多表查询怎么处理？例如，查看账单时，希望现实菜品名称

查询的结果从上图变为下图：

day03-2-拓展

方案一

由多张表组合查询的的结果，我们仍然可以将其映射成一个Javabean

例如MultTableBean类，该类的属性可以来自多张表的字段，即该类跟多张表进行映射

在这基础上，仍然可以使用之前的想法：在Dao层创建一个新的dao类，该类专门用于多表操作，在service层也创建相应的service类（根据实际情况），供界面层调用等

day03-2-拓展

方案二

DBUtils数据库连接池多表连接查询-CSDN博客

5.1方案一完成多表查询

5.1.1代码实现

1.创建MultiTableBean类

package com.li.mhl.domain;

import java.util.Date;

public class MultiTableBean {
    private Integer id;
    private String billId;
    private Integer menuId;
    private Integer nums;
    private Double money;
    private Integer diningTableId;
    private Date billDate;
    private String state;
    //增加menu表的字段
    private String name;
    private Double price;

    public MultiTableBean() {
    }

    public MultiTableBean(Integer id, String billId, Integer menuId, Integer nums, Double money, Integer diningTableId, Date billDate, String state, String name, Double price) {
        this.id = id;
        this.billId = billId;
        this.menuId = menuId;
        this.nums = nums;
        this.money = money;
        this.diningTableId = diningTableId;
        this.billDate = billDate;
        this.state = state;
        this.name = name;
        this.price = price;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getBillId() {
        return billId;
    }

    public void setBillId(String billId) {
        this.billId = billId;
    }

    public Integer getMenuId() {
        return menuId;
    }

    public void setMenuId(Integer menuId) {
        this.menuId = menuId;
    }

    public Integer getNums() {
        return nums;
    }

    public void setNums(Integer nums) {
        this.nums = nums;
    }

    public Double getMoney() {
        return money;
    }

    public void setMoney(Double money) {
        this.money = money;
    }

    public Integer getDiningTableId() {
        return diningTableId;
    }

    public void setDiningTableId(Integer diningTableId) {
        this.diningTableId = diningTableId;
    }

    public Date getBillDate() {
        return billDate;
    }

    public void setBillDate(Date billDate) {
        this.billDate = billDate;
    }

    public String getState() {
        return state;
    }

    public void setState(String state) {
        this.state = state;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return id +
                "\t\t" + menuId +
                "\t\t\t" + name +
                "\t\t" + price +
                "\t\t" + nums +
                "\t\t\t" + money +
                "\t\t" + diningTableId +
                "\t\t" + billDate +
                "\t\t" + state;
    }
}

2.创建MultiTableDAO类

package com.li.mhl.dao;

import com.li.mhl.domain.MultiTableBean;

/**
 * @author 李
 * @version 1.0
 */
public class MultiTableDAO extends BasicDAO<MultiTableBean>{

}

3.修改BillService类

这里为了简单，不再创建MultiTableService，直接在BillService类中增加方法

修改处1：

//定义MultiTableDAO属性
private MultiTableDAO multiTableDAO = new MultiTableDAO();

修改处2：

//改进后的方法--返回所有的账单，提供给View使用
public List<MultiTableBean> list2() {
    return multiTableDAO.queryMulti("SELECT " +
                    "bill.id,menuId,NAME,price,nums,money,diningTableId,state,billDate " +
                    "FROM bill,menu WHERE menuId=menu.id",
            MultiTableBean.class);
}

4.修改MHLView类

修改处1：在该类中增加方法listBill2()

//显示账单信息-改进
public void listBill2() {
    List<MultiTableBean> multiTableBeans = billService.list2();
    System.out.println("\n编号\t\t菜品号\t\t菜品名\t\t单价\t\t\t菜品量\t\t金额\t\t\t桌号\t\t日期\t\t\t\t\t\t\t状态");
    for (MultiTableBean multiTableBean : multiTableBeans) {
        System.out.println(multiTableBean);
    }
    System.out.println("============显示完毕============");
}

修改处2：在里层循环中调用该方法

day03-2-拓展