无法更新asp.net

本文介绍了无法更新asp-core 2.2 c#中的记录的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我正在尝试如下更新项目的记录

I am trying to update the record of an item as follows

[HttpPost] [ValidateAntiForgeryToken] public async Task<IActionResult> Edit(int id, [Bind("Id,Label,Description,LessonId,Position,FileName,Format,Status")] Content content) { if (id != content.Id) { return NotFound(); } var existingContent = await _context.Contents.FindAsync(id).ConfigureAwait(false); if (existingContent == null) { return NotFound(); } string fileToDelete = null; if (ModelState.IsValid) { try { if (Request.Form.Files["FileName"] != null) { IFormFile uploadedFile = Request.Form.Files["FileName"]; var lesson_mimetype = uploadedFile.ContentType; string[] extensions = new string[] { ".jpeg", ".jpg", ".gif", ".png", ".mp4", ".mp3", ".pdf" }; ResponseMsg fileTypeValidationMsg = FileUploadHelper.ValidateFileExtension(uploadedFile, extensions); if (!fileTypeValidationMsg.ResponseStatus) { ModelState.AddModelError("FileName", fileTypeValidationMsg.ResponseDescription); } ResponseMsg filesizeValidationMsg = FileUploadHelper.ValidateFilesize(uploadedFile, 200); if (!filesizeValidationMsg.ResponseStatus) { ModelState.AddModelError("FileName", filesizeValidationMsg.ResponseDescription); } if (content.Format == ResourceFormat.Text) { string desiredUploadDirectory = "TextResources"; string lesson_file_name = await uploadHelper.SaveFileAsync(Request.Form.Files["FileName"], desiredUploadDirectory).ConfigureAwait(false); existingContent.TextFileUrl = desiredUploadDirectory + "/" + lesson_file_name; existingContent.FileName = lesson_file_name; fileToDelete = existingContent.TextFileUrl; } else { string desiredUploadDirectory = "MultimediaResources"; string lesson_file_name = await uploadHelper.SaveFileAsync(Request.Form.Files["FileName"], desiredUploadDirectory).ConfigureAwait(false); existingContent.MultiMediaFileUrl = desiredUploadDirectory + "/" + lesson_file_name; existingContent.FileName = lesson_file_name; fileToDelete = existingContent.MultiMediaFileUrl; } } existingContent.LastUpdated = DateTime.Now; existingContent.Label = content.Label; existingContent.Description = content.Description; existingContent.LessonId = content.LessonId; existingContent.Position = content.Position; existingContent.Status = content.Status; existingContent.Format = content.Format; //_context.Update(existingContent); Now removed for the code to work await _context.SaveChangesAsync().ConfigureAwait(false); if (fileToDelete != null) { System.IO.File.Delete(fileToDelete); } return RedirectToAction(nameof(Index)); } catch (Exception e) { ModelState.AddModelError("", e.Message); } } ViewData["LessonId"] = new SelectList(_context.Lessons, "Id", "Label", content.LessonId); return View(content); }

但是问题是，当我提交更新表单时，出现以下错误消息

But the problem is that when I submit the form for the update, I get the following error message

无法跟踪实体类型'Content'的实例，因为已经跟踪了具有相同键值的{'Id'}的另一个实例.附加现有实体时，请确保仅附加一个具有给定键值的实体实例.考虑使用'DbContextOptionsBuilder.EnableSensitiveDataLogging'来查看冲突的键值.

The instance of entity type 'Content' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.

我不知道该如何解决.我将不胜感激任何向导.

I do not know how to resolve this. I will appreciate any guide please.

推荐答案

在大多数情况下，EF会自动检测哪些字段需要更新，并且在上下文中(带有实体)具有update函数是对说您正在尝试做不必要的事情.

In most cases, EF will automatically detect which fields need updating, having an update function in a context (that takes an entity) is a red flag to say you are trying to do something that is not required.

EF在幕后做了很多事情，因此您不必考虑它们.这就是其中之一.

EF does a lot of things behind the scenes, so you don't have to think about them. This is one of them.

我怀疑您读了一个非常老的博客，内容涉及10年前某人必须如何做才能使EF更新记录.

I suspect you read a really old blog about how someone 10 years ago had to do something to get EF to update a record.

此外，从上下文类中删除该update函数，以便没有其他人绊倒它.

Also, remove that update function from your context class, so that no-one else trips up on it.