如何使用实体框架和身份解决对象处置异常ASP.NET Core [英] How to resolve object disposed exception ASP.NET Core with Entity Framework and Identity

问题描述

我正在尝试编写一个控制器，该控制器从AJAX调用接收请求，并通过DBContext对数据库执行一些调用.但是，当我将命令var user = await GetCurrentUserAsynch();放在对DBContext的任何调用之前时，如下所示，我得到一个ObjectDisposedException(无法访问已处置的对象).

I am trying to write a controller that receives a request from an AJAX call and performs some calls to the database via the DBContext. However, when I place the command var user = await GetCurrentUserAsynch(); in front of any calls to the DBContext, as shown below, I get an ObjectDisposedException (Cannot access a disposed object).

似乎UserManager和DBContext不能很好地配合使用，但是我在此问题上找不到很多信息.

It appears to be the UserManager and the DBContext not playing nicely together, however I can't find much information on the matter.

[HttpPost]        
public async void EditUserMapItemAjax([FromBody]UserMapItemViewModel userMapItemViewModel)
{            
    var user = await GetCurrentUserAsync();
    var mapItem = _db.MapItems.SingleOrDefault(x => x.Id == userMapItemViewModel.MapItemId);   

    ...
}

private Task<ApplicationUser> GetCurrentUserAsync() => _userManager.GetUserAsync(HttpContext.User);

推荐答案

将您的控制器操作声明为async Task，而不是async void.

Declare your controller action as async Task, not async void.

对于后者，一旦您的方法命中第一个await，它将控制权返回给调用者，并且由于ASP.NET现在无法跟踪其进度(就像它返回)，它会处理您的控制器实例，并(最有可能)与它一起放置任何本地作用域的字段.

With the latter, as soon as your method hits the first await, it returns control to the caller, and because ASP.NET now has no way to track its progress (as it would have when it returns a Task instead), it disposes your controller instance, and (most-likely) along with it any locally-scoped fields.

尽管在那里，因为无论如何都处于异步方法中，所以您应该更喜欢EF调用的异步版本；即await _db.MapItems.SingleOrDefaultAsync()

While you're there, as you're in an async method anyway, you should prefer the async version of the EF call; i.e. await _db.MapItems.SingleOrDefaultAsync()

这篇关于如何使用实体框架和身份解决对象处置异常ASP.NET Core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！