如何在不插入新对象的情况下从数据库更新对象？
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【中文标题】如何在不插入新对象的情况下从数据库更新对象？【英文标题】：How can I update object from database without inserting new? 【发布时间】：2021-04-28 02:38:14 【问题描述】：我想从我的数据库中更新对象而不向数据库插入新对象。
这里有两种方法：
@RequestMapping("/edit/id")
public ModelAndView showEditProductPage(@PathVariable(name = "id") Integer id, Model model)
ModelAndView modelAndView = new ModelAndView("edit_customer");
Customer customer = customerService.getCustomer(id);
//Customer customer = customerRepository.getOne(id);
//customer.setCustomerId(customerRepository.getOne(id).getCustomerId());
System.out.println(customer.getCustomerId());
System.out.println(customer.toString());
model.addAttribute("customer", customer);
modelAndView.addObject("customer", customer);
return modelAndView;
输出为：id=1 Customerid=1, firstName='Krzysztof', address='ulica 1', phoneNumber='123456789'
@RequestMapping("/update/id")
public String updateCustomer(@PathVariable(name = "id") Integer id,
@ModelAttribute("customer") Customer customer)
//System.out.println(id);
//customer.setCustomerId(id);
System.out.println("____________________");
System.out.println("customer id " + customer.getCustomerId());
System.out.println("____________________");
customer.setCustomerId(id);
System.out.println("customer id " + customer.getCustomerId());
System.out.println("owner " + customer.getOwner());
System.out.println("address " + customer.getAddress());
System.out.println("phone number " + customer.getAddress());
System.out.println("to string: " + customer.toString());
System.out.println("id " + id);
customerService.save(customer);
return "redirect:/";
第二种方法后的输出是：id=1 Customerid=null, firstName='Krzysztof', address='ulica 1zzz', phoneNumber='123456789'
客户存储库扩展了 JPA 存储库， 保存方法：
public void save(Customer customer)
customerRepository.save(customer);
百里香模板：
!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="utf-8" />
<title>Edit Customer</title>
<link rel="stylesheet" type="text/css" th:href="@/table.css" />
</head>
<body>
<div align="center">
<h1>Edit Customer</h1>
<a href="/">Go Back</a>
<br />
<form action="#" th:action="@'/update/' + $id" th:object="$customer"
method="post">
<table border="0" cellpadding="10">
<tr>
<td>Customer ID:</td>
<td>
<input type="text" th:field="*customerId" readonly="readonly" />
</td>
</tr>
<tr>
<td>First Name:</td>
<td>
<input type="text" th:field="*owner" />
</td>
</tr>
<tr>
<td>Address:</td>
<td><input type="text" th:field="*address" /></td>
</tr>
<tr>
<td>Phone Number:</td>
<td><input type="text" th:field="*phoneNumber" /></td>
</tr>
<tr>
<td colspan="2"><button type="submit">Save</button> </td>
</tr>
</table>
</form>
</div>
</body>
</html>
客户实体类：
package com.praca.manager.entity;
import javax.persistence.*;
import java.util.List;
@Entity
@Table(name = "customer")
public class Customer
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer customerId;
@Column(name = "owner")
private String owner;
@Column(name = "address")
private String address;
@Column(name = "phone_number")
private String phoneNumber;
@OneToMany(mappedBy = "customer")
List<Details> details;
public Customer()
public Customer(Integer customerId,
String owner,
String address,
String phoneNumber)
this.customerId = customerId;
this.owner = owner;
this.address = address;
this.phoneNumber = phoneNumber;
public Integer getCustomerId()
return customerId;
public void setCustomerId(Integer id)
this.customerId = customerId;
public String getOwner()
return owner;
public void setOwner(String firstName)
this.owner = firstName;
public String getAddress()
return address;
public void setAddress(String address)
this.address = address;
public String getPhoneNumber()
return phoneNumber;
public void setPhoneNumber(String phoneNumber)
this.phoneNumber = phoneNumber;
@Override
public String toString()
return "Customer" +
"id=" + customerId +
", firstName='" + owner + '\'' +
", address='" + address + '\'' +
", phoneNumber='" + phoneNumber + '\'' +
'';
这里的 ID 字段也是 '1' sql脚本：
create table customer(
customer_id int auto_increment primary key not null,
owner varchar(200) not null,
address varchar(200) not null,
phone_number int not null
);
尽管我尝试将 id 设置为 1 或任何其他数字，但它仍然为空。 谁能告诉我为什么以及如何解决它？
【问题讨论】：
发布你的Customer实体类
我怀疑你的 id 生成策略有问题，我猜你的 id 不是 autoincrement？
贴在原帖底部
它是自增的，我一会儿用sql编辑帖子
设置这个：@GeneratedValue(strategy = GenerationType.AUTO)
【参考方案1】：
问题出在 Customer 类的设置器中：
public void setCustomerId(Integer id)
this.customerId = customerId;
您将该字段分配给它自己，这就是它始终为空的原因。应该是“this.customerId = id”:)。
【讨论】：
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