无法访问已处置的对象。导致此错误的常见原因是处理上下文 [英] Cannot access a disposed object. A common cause of this error is disposing a context
问题描述
我已经编写了一个简单的应用程序，当我导航到编辑页面时，弹出以下错误。
I have written a simple application and when I navigate to my edit page the below error pops up.
Microsoft.EntityFrameworkCore.Query [10100]
Microsoft.EntityFrameworkCore.Query[10100]
遍历上下文类型 app.Models.ApplicationDbContext的查询结果时发生异常。
An exception occurred while iterating over the results of a query for context type 'app.Models.ApplicationDbContext'.
System.ObjectDisposedException：无法访问已处置的对象。导致此错误的常见原因是，处理从依赖项注入中解决的上下文，然后稍后尝试在应用程序中的其他位置使用相同的上下文实例。如果在上下文上调用Dispose（）或将上下文包装在using语句中，则可能会发生这种情况。如果您使用的是依赖注入，则应该让依赖注入容器负责处理上下文实例。
System.ObjectDisposedException: Cannot access a disposed object. A common cause of this error is disposing a context that was resolved from dependency injection and then later trying to use the same context instance elsewhere in your application. This may occur if you are calling Dispose() on the context, or wrapping the context in a using statement. If you are using dependency injection, you should let the dependency injection container take care of disposing context instances.
似乎EF证明了我无法理解的有用信息。该错误的棘手部分是，当我导航到编辑页面时，它会随机发生。有时它可以工作，有时它无法加载 Edit.cshtml 上的某些属性，但仍然可以工作，有时应用程序崩溃，仅在我的控制台中提供了错误。另一个奇怪的情况是它不会产生任何 500 或 5xx 错误。
It seems EF is proving a useful information which I can not understand. The tricky part of this error is that it happens randomly when I navigate to the edit page. Sometime it works, Sometimes it fails to load some properties on Edit.cshtml but still works and sometimes the application crashes with provided error just in my console. Another strange happen is that it dose not generate any 500 or 5xx error. It just simply crashes and stop the application.
这是我的 Edit.cshtml 内容：
@page
@model EditModel
@{
ViewData["Title"] = "Edit Book";
}
<h2>Edit Book</h2>
<div class="row justify-content-center">
<div class="col-md-6">
<form method="post" class="form-border">
<div asp-validation-summary="All" class="validation-container alert alert-danger"></div>
<div class="form-group">
<label asp-for="Book.Name"></label>
<input asp-for="Book.Name" class="form-control" />
<span class="form-text text-danger" asp-validation-for="Book.Name"></span>
</div>
<div class="form-group">
<label asp-for="Book.Description"></label>
<input asp-for="Book.Description" class="form-control" />
</div>
<div class="form-group">
<label asp-for="Book.Author"></label>
<input asp-for="Book.Author" class="form-control" />
</div>
<input asp-for="Book.Id" type="hidden">
<button type="submit" class="btn btn-primary">Update</button>
<a asp-page="Index" class="btn btn-success">Back To List</a>
</form>
</div>
</div>
这是我的 Edit.cshtm.cs OnGet 方法：
public async void OnGet(int id)
{
Book = await _db.Books.SingleOrDefaultAsync(x => x.Id == id);
if(Book == null)
{
RedirectToPage("Index");
}
}
我正在使用 .Net核心2.2.104
当我运行命令 dotnet ef --version 时，它生成 Entity Framework Core .NET命令行工具
2.2.2-servicing-10034
Also when I run command dotnet ef --version it generates Entity Framework Core .NET Command-line Tools
2.2.2-servicing-10034
推荐答案
这是因为您的方法返回类型为 async void 。通常，在代码中使用 async void 时，这是个坏消息，因为：
This is because of your method return type async void. In general, when you are using async void in your code it’s bad news, because:
- 您不能等待其完成
- 任何未处理的异常都会终止您的进程（哎呀！）
因此从您的方法中返回 async Task 而不是 async void ，如下所示：
So return async Task instead of async void from your method as follows:
public async Task OnGet(int id)
{
Book = await _db.Books.SingleOrDefaultAsync(x => x.Id == id);
if(Book == null)
{
RedirectToPage("Index");
}
}
更多详细信息：
在以下情况下无法访问ASP.NET Core中已处置的对象注入DbContext
这篇关于无法访问已处置的对象。导致此错误的常见原因是处理上下文的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
