.Net Core DBContext 依赖注入答案

【问题标题】：.Net Core DBContext dependency injection.Net Core DBContext 依赖注入
【发布时间】：2021-10-23 08:11:24
【问题描述】：

我已经重构了我的代码，以尽量避免根据MS Instructions 和本网站上的其他帖子出现以下错误，它似乎略有改善，但如果我快速连续单击多个按钮，我我仍然收到以下错误：

A second operation started on this context before a previous operation completed. This is usually caused by different threads using the same instance of DbContext, however instance members are not guaranteed to be thread safe.

startup.cs

services.AddDbContext<ApplicationDbContext>(options => options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

在我的控制器中：

readonly RGWIncrementUserActionClicks RGWIncrementClicks = new();
private readonly ApplicationDbContext _context;

public RGWController(IEmailSender emailSender, ApplicationDbContext context)
{
_emailSender = emailSender;
_context = context;
}

public async Task <IActionResult> RGWInsertNewActionNumber(int actionNumber)
{
string userId = ClaimsPrincipalExtensions.GetUserId<string>(User);

await RGWIncrementClicks.UserClick(actionNumber, userId, _context);

return RedirectToAction("RGW");
}

当await RGWIncrementClicks.UserClick(actionNumber, userId, _context);被触发时，UserClick方法（未显示）有一个switch语句，可以调用其他方法的组合，根据传入的actionNumber参数向DB添加值。

我使用 await 尝试了所有后续方法和调用，但仍然出现多线程错误。我也尝试过不使用它们，但仍然出现多线程错误。

我不明白的是await RGWIncrementClicks.UserClick(actionNumber, userId, _context);是所有使用dbContext的后续函数的入口点，它使用await，加上它为这个调用实例传入了注入的dbContext，所以我如何我在后续函数中遇到线程错误...它们应该只在此处等待入口点完成后触发第二次，表明所有后续函数都已完成...不是吗？

更新：我只是在想我实际上并不希望它是异步的，因为我希望 UI 在数据库更改后触发 RedirectToAction 时在每次用户点击时更新.所以也许这不是线程管理问题，而是用户管理问题....我应该防止用户在触发我的RGWInsertNewActionNumber 方法的任何按钮上单击两次...

Update.2 - 为了节省空间，我把它省略了：

public class RGWIncrementUserActionClicks
{
private static readonly IncrementSiteActions _IncrementSiteActions = new();
private static readonly IncrementUserActions _IncrementUserActions = new();

public async Task UserClick(int actionNumber, string userId, ApplicationDbContext _context)
        {
var userActions = await _context.UserEnvironmentalActionCounts.FindAsync(userId);
var siteTotalActions = await _context.SiteEnvironmentalActionCounts.FirstOrDefaultAsync();

siteTotalActions.SiteGlobalWarmingClicks++;

switch (actionNumber)
{
case 1:

if (userActions != null)
{
await _IncrementUserActions.incrementUserActions(userId, userActions => { userActions.ReduceMeat++; userActions.UserReduceMeatCO2Total = userActions.UserReduceMeatCO2Total + 2.0075; }, userActions => { userActions.UserCO2Total = userActions.UserCO2Total + 2.0075; });

if (siteTotalActions != null)
{
await _IncrementSiteActions.incrementSiteActions(siteTotalActions => { siteTotalActions.SiteReduceMeat++; }, true, true, true);
}
else
{
await _context.SiteEnvironmentalActionCounts.AddAsync(new SiteEnvironmentalActionCounts { SiteTotal = 1, SiteGlobalWarmingTotal = 1, SiteReduceMeat = 1, SiteDeforestationTotal = 1, SiteExtinctionTotal = 1 });
}
}
else
{
await _context.UserEnvironmentalActionCounts.AddAsync(new UserEnvironmentalActionCounts { Id = userId, ReduceMeat = 1, UserTotal = 1, UserReduceMeatCO2Total = 2.0075, UserCO2Total = 2.0075 });

if (siteTotalActions != null)
{
await _IncrementSiteActions.incrementSiteActions(siteTotalActions => { siteTotalActions.SiteReduceMeat++; }, true, true, true);
}
else
{
await _context.SiteEnvironmentalActionCounts.AddAsync(new SiteEnvironmentalActionCounts { SiteTotal = 1, SiteGlobalWarmingTotal = 1, SiteReduceMeat = 1, SiteDeforestationTotal = 1, SiteExtinctionTotal = 1 });
}
}
await _context.SaveChangesAsync();
break;

case 2:

...etc.

default:
break;
            }
        }
    }
}

错误详情：

Microsoft.EntityFrameworkCore.DbContext.SaveChangesAsync(bool acceptAllChangesOnSuccess, CancellationToken cancellationToken)
GatheringForGood.Areas.FunctionalLogic.IncrementUserActions.incrementUserActions(string userId, Action<UserEnvironmentalActionCounts> update, Action<UserEnvironmentalActionCounts> updateUserCO2Total) in IncrementUserActions.cs
+
23. await _context.SaveChangesAsync();
GatheringForGood.Areas.FunctionalLogic.RGWIncrementUserActionClicks.UserClick(int actionNumber, string userId, ApplicationDbContext _context) in RGWIncrementUserActionClicks.cs
+
30. await _IncrementUserActions.incrementUserActions(userId, userActions => { userActions.ReduceMeat++; userActions.UserReduceMeatCO2Total = userActions.UserReduceMeatCO2Total + 2.0075; }, userActions => { userActions.UserCO2Total = userActions.UserCO2Total + 2.0075; });
MyApp.Controllers.ReduceGlobalWarmingController.RGWInsertNewActionNumber(int actionNumber) in ReduceGlobalWarmingController.cs
+
            354. await RGWIncrementClicks.UserClick(actionNumber, userId, _context);
Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor+TaskOfIActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, object controller, object[] arguments)
System.Threading.Tasks.ValueTask<TResult>.get_Result()

【问题讨论】：

你必须至少显示 RGWIncrementClicks.UserClick。
谢谢，现在更新@Serge

标签： c# asp.net thread-safety dbcontext

【解决方案1】：

尝试替换

private static readonly IncrementSiteActions _IncrementSiteActions = ....
private static readonly IncrementUserActions _IncrementUserActions = ....

非静态的

private  readonly IncrementSiteActions _IncrementSiteActions = ....
private  readonly IncrementUserActions _IncrementUserActions = ....

【讨论】：

【解决方案2】：

我决定避免使用 javascript 多次点击 UI 层。我对此有一个小问题，但它已解决。如果其他人需要防止多次 UI 点击，请在此处了解更多信息。

JS function for a number of elements onclick without using getElementById

【讨论】：