想要将更改保存到数据库时出现异常

Posted 2023-04-12

【中文标题】想要将更改保存到数据库时出现异常

【英文标题】：Getting Exception when want to Save Changes to database

【发布时间】：2021-07-21 23:51:02

【问题描述】：

当我想更改客户端输入的数据库中的值时出现异常。 这是我数据库https://ibb.co/q1cwwYq 中的所有客户，当我单击一个客户时，我将客户重定向到编辑视图，看起来像这样https://ibb.co/NSfvnGg。现在，当我单击保存按钮时，我收到错误 System.Data.Entity.Infrastructure.DbUpdateException: 'An error occurred while updating the entries. See the inner exception for details.'

SqlException: The UPDATE statement conflicted with the FOREIGN KEY constraint "FK_dbo.Customers_dbo.MemberShipTypes_MemberShipTypeID". The conflict occurred in database "Vidly.Models.ApplicationDbContext", table "dbo.MemberShipTypes", column 'Id'.
The statement has been terminated.

这是我的客户表格

@model Vidly.Models.NewCustomerViewModel
@
    ViewBag.Title = "New";
    Layout = "~/Views/Shared/_Layout.cshtml";


<h2>New Customer</h2>

@using (Html.BeginForm("Save", "Customer"))

    <div class="form-group">
        @Html.LabelFor(m => m.Customer.Name)
        @Html.TextBoxFor(m => m.Customer.Name, new  @class = "form-control" )
    </div>

    <div class="form-group">
        @Html.LabelFor(m => m.Customer.Birthdate)
        @Html.TextBoxFor(m => m.Customer.Birthdate,"0:d MMM yyyy", new  @class = "form-control" )
    </div>

   

    <div class="form-group">
        @Html.LabelFor(m => m.Customer.MemberShipTypeID)
        @Html.DropDownListFor(m => m.Customer.MemberShipType,new SelectList(Model.MemberShipTypes,"ID","Name"),"", new  @class = "form-control" )
    </div>

    <div class="checkbox">
        <label>
            @Html.CheckBoxFor(m => m.Customer.IsSubscribedToNewsLetter) Subscribed to Newsletter?
        </label>
    </div>

    @Html.HiddenFor(m => m.Customer.Id);

    <button type="submit" class="btn btn-primary">Save</button>

在 CustomerController 中保存操作

public ActionResult Save(Customer customer)
           
            if(customer.Id == 0)
                _context.Customers.Add(customer);
            else
            
                var customerInDb = _context.Customers.Single(c => c.Id == customer.Id);

                customerInDb.Name = customer.Name;
                customerInDb.Birthdate = customer.Birthdate;
                customerInDb.IsSubscribedToNewsLetter = customer.IsSubscribedToNewsLetter;
                customerInDb.MemberShipTypeID = customer.MemberShipTypeID;


            
            _context.SaveChanges();


            return RedirectToAction("Customers", "Customer");
        

客户类别

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Web;

namespace Vidly.Models

    public class Customer
    
        
        public int Id  get; set; 
        [Required] [StringLength(255)]
        public  string  Name  get; set; 

        public bool IsSubscribedToNewsLetter  get; set; 

        public MemberShipType MemberShipType  get; set; 

        [Display(Name = "Membership Type")]
        public byte MemberShipTypeID  get; set; 

        [Display(Name = "Date of Birth")]
        public DateTime? Birthdate  get; set; 



    

我在代码的_context.SaveChanges(); 这一行遇到错误。

【问题讨论】：

你有什么错误？

发布完整的异常文本，而不仅仅是消息的一部分。您可以使用Exception.ToString() 或在调试时单击异常弹出窗口中的Copy Details 轻松获取全文。正如消息所说：See the inner exception for details.

@PanagiotisKanavos SqlException: The UPDATE statement conflicted with the FOREIGN KEY constraint "FK_dbo.Customers_dbo.MemberShipTypes_MemberShipTypeID". The conflict occurred in database "Vidly.Models.ApplicationDbContext", table "dbo.MemberShipTypes", column 'Id'. The statement has been terminated.

该错误表明MembershipTypeID 值无效。该代码试图存储MembershipTypes 表中不存在的值

@PanagiotisKanavos 好的，我更改了customerInDb.MemberShipTypeID = customer.MemberShipTypeID，但现在我收到了Vidly.Models.Customer.MemberShipType.get returned null. System.NullReferenceException: 'Object reference not set to an instance of an object.'

【参考方案1】：

你有错误

@Html.DropDownListFor(m => m.Customer.MemberShipType,new SelectList(Model.MemberShipTypes,"ID","Name"),"", new  @class = "form-control" )

应该是

@Html.DropDownListFor(m => m.Customer.MemberShipTypeId,new SelectList(Model.MemberShipTypes,"ID","Name"),"", new  @class = "form-control" )

这就是您的 Customer.MemberShipTypeId 值无效且无法更新的原因。

也可以更新试试这个代码：

 var customerInDb = _context.Customers.FirstOrDefault(c => c.Id == customer.Id);

if (customerInDb !=null)


  customerInDb.Name = customer.Name;
    customerInDb.Birthdate = customer.Birthdate;
   customerInDb.IsSubscribedToNewsLetter = customer.IsSubscribedToNewsLetter;
 customerInDb.MemberShipTypeID = customer.MemberShipTypeID;

_context.Entry(CustomerInDb).State = EntityState.Modified;


....

 _context.SaveChanges();

【讨论】：

对象已经处于Modified 状态，这就是为什么尝试更新而不是插入