c# - "An entity object cannot be referenced by multiple instances of IEntityChangeTracker"

我有 3 个数据库表:Vendors、Regions 和 VendorRegions:

Vendors
-------------------
VendorID (PK)
Name

Regions
-------------------
RegionID (PK)
Name

VendorRegions
-------------------
VendorID (PK)
RegionID (PK)

在我创建供应商的页面上，我在复选框列表中列出了每个区域。对于检查的每个区域，我想将 VendorID 和 RegionID 添加到 VendorRegions 表中。

我正在使用 Entity Framework 、C# 和 MVC 3。

这是我的 Controller 代码:

public class VendorsController : Controller
{
    readonly IVendorsRepository _vendorsRepository;
    readonly IRegionsRepository _regionsRepository;

    public VendorsController()
    {
        _vendorsRepository = new SqlVendorsRepository();
        _regionsRepository = new SqlRegionsRepository();
    }

    [HttpPost]
    public ActionResult Create(VendorViewModel viewModel, string[] Regions)
    {
        var vendor = new Vendor();
        TryUpdateModel(vendor);

        if (ModelState.IsValid)
        {
            vendor.Regions.Clear();
            foreach (var regionId in Regions)
            {
                vendor.Regions.Add(_regionsRepository.GetRegion(Int32.Parse(regionId)));
            }

            _vendorsRepository.SaveVendor(vendor);
            return RedirectToAction("Index");
        }

        return View(viewModel);     // validation error, so redisplay same view
    }
}

这是我的供应商存储库代码:

public class SqlVendorsRepository : IVendorsRepository
{
    private readonly MyDBEntities _entities;

    public SqlVendorsRepository()
    {
        _entities = new MyDBEntities();
    }


    public void SaveVendor(Vendor vendor)
    {
        // If it's a new vendor, just attach it to the DataContext
        if (vendor.VendorID == 0)
            _entities.Vendors.Context.AddObject("Vendors", vendor); // ERROR HERE
        else if (vendor.EntityState == EntityState.Detached)
        {
            // We're updating an existing vendor, but it's not attached to this data context, so attach it and detect the changes
            _entities.Vendors.Context.Attach(vendor);
            _entities.Vendors.Context.Refresh(System.Data.Objects.RefreshMode.ClientWins, vendor);
        }
        _entities.Vendors.Context.SaveChanges();
    }
}

当我尝试在 _entities.Vendors.Context.AddObject("Vendors", vendor); 处保存我的供应商时发生错误。以防万一，这是我的 Regions 存储库代码:

public class SqlRegionsRepository : IRegionsRepository
{
    private readonly MyDBEntities _entities;

    public SqlRegionsRepository()
    {
        _entities = new MyDBEntities();
    }


    public IQueryable<Region> Regions
    {
        get { return _entities.Regions.AsQueryable(); }
    }


    public Region GetRegion(int id)
    {
        return Regions.FirstOrDefault(st => st.RegionID == id);
    }
}

这似乎是一件简单的事情，但我不知道如何克服这个错误。有任何想法吗？

最佳答案

您有两个不同的存储库，每个存储库都有一个 单独的 数据上下文 - 这是根本问题 - 您的数据上下文应该由所有存储库共享，即您可以通过构造函数注入(inject)来注入(inject)它:

MyDBEntities entities = new MyDBEntities();
_vendorsRepository = new SqlVendorsRepository(entities);
_regionsRepository = new SqlRegionsRepository(entities);

关于c# - "An entity object cannot be referenced by multiple instances of IEntityChangeTracker"，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/7152773/