为什么我的实体被多个 IEntityChangeTracker 实例引用？

Question

我正在尝试通过将我的 DbContext 注入服务类来在我的 ASP.NET Web 窗体项目中实现现代实践（使用服务、IoC 等），但我一直收到一条错误消息An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

这让我很困惑，因为我相对确定我只有一个 DbContext 跟踪更改。

有什么问题？我正在使用将 DbContext 作为函数参数发送到的静态类，但除此之外，我没有在页面端进行任何更改...

public partial class Create : System.Web.UI.Page

{

    private LicenseService licenseService;

    private ApplicationDbContext context = new ApplicationDbContext();

    protected void Page_Load(object sender, EventArgs e)

    {

        try

        {

            licenseService = new LicenseService(context);

        }

        catch (Exception ex)

        {

            // TODO Add error handling/logging.

            ErrorMessage.Text = ex.Message;

        }

    }

    protected void Page_LoadComplete(object sender, EventArgs e)

    {

        this.context.Dispose();

    }

    protected async void Save_Click(object sender, EventArgs e)

    {

        try

        {

            var userManager = Request.GetOwinContext().GetUserManager<ApplicationUserManager>();

            var user = await userManager.FindByIdAsync(User.Identity.GetUserId());

            await SaveLicenseAsync(user);

            // Show a message that the work was done.

            ShowSnackbar("License was successfully added; redirecting...", "Default");

        }

        catch (Exception ex)

        {

            // TODO Add error handling/logging.

            ErrorMessage.Text = ex.Message;

        }

    }

    private async Task SaveLicenseAsync(ApplicationUser user)

    {

        // Get the specified expiry date.

        DateTime.TryParse(ExpiryDatePicker.SelectedDate.ToString(), out DateTime expiryDate);

        // Create the viewmodel that will be passed to the service.

        var model = new LicenseViewModel

        {

            ExpiryDate = expiryDate,

            Name = NameTextBox.Text

        };

        await licenseService.AddAsync(model, user);

    }

}

我的服务通常包含与 EF 的所有交互。我喜欢这个，因为它将页面与 DbContext 逻辑分开。

Answer 1

问题将与您在许可证中的用户参考有关。这是从 Owin 上下文中检索到的，但您正在尝试将其保存/关联到您的许可证上下文。我将更新该方法以简单地接受用户 ID，然后从您的许可证上下文加载并关联用户。public async Task AddRangeAsync(IEnumerable<LicenseViewModel> models, int ownerId){&nbsp; &nbsp; var list = new List<License>();&nbsp; &nbsp; var owner = context.Users.Single(x => x.UserId == ownerId);&nbsp; &nbsp; foreach (var model in models)&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; list.Add(new License&nbsp; &nbsp; &nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ExpiryDate = model.ExpiryDate,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Name = model.Name,&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; User = owner&nbsp; &nbsp; &nbsp; &nbsp; });&nbsp; &nbsp; }&nbsp; &nbsp; context.Licenses.AddRange(list);&nbsp; &nbsp; await context.SaveChangesAsync();}那应该可以解决您的问题。偷偷摸摸的小细节。:)为了避免负载，您可以使用：var owner = context.Owners.Local.SingleOrDefault(x => x.UserId == ownerId);if (owner == null){&nbsp; &nbsp; owner = new User{UserId = ownerId};&nbsp; &nbsp; context.Users.Attach(owner);}// ...我可能会考虑将其放在基类方法中以从上下文中检索所有者引用。该方法的警告是，除非您从数据库显式加载，否则此上下文中的用户将不包含有关用户的详细信息。（即名称等）因此，只要团队知道不相信上下文将具有完整的用户，除非明确重新加载，就可以从性能 PoV 中获得。