＆QUOT;一个实体对象不能由IEntityChangeTracker＆QUOT的多个实例被引用; [英] "An entity object cannot be referenced by multiple instances of IEntityChangeTracker"

问题描述

我有3个数据库表：供应商，各地区，各VendorRegions：

I have 3 database tables: Vendors, Regions, and VendorRegions:

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

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

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

在我的网页创建一个供应商，我列出了每区一个复选框列表。对于每一个被选中区域，我想的厂商ID和RegionID添加到VendorRegions表。

On my page to create a vendor, I list out every Region in a checkbox list. For every region that is checked, I'd like to add the VendorID and RegionID to the VendorRegions table.

我使用实体框架，C＃和MVC 3。

I'm using Entity Framework, C# and MVC 3.

下面是我的控制器code：

Here's my controller code:

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
    }
}

下面是我的供应商库code：

Here's my Vendors repository code:

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();
    }
}

当我尝试保存我的供应商，在 _entities.Vendors.Context.AddObject（「卖方」，供应商）出现错误; 。以防万一，这是我区资源库code：

The error occurs when I try to save my vendor, at _entities.Vendors.Context.AddObject("Vendors", vendor);. And just in case, here's my Regions repository code:

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);
    }
}

这似乎是一个简单的事情，但我不知道如何让过去的这个错误。任何想法？

This seems like a simple thing to do, but I don't know how to get past this error. Any ideas?

推荐答案

您有两个不同的版本库，每有一个独立数据上下文 - 这是根本的问题 - 你的数据上下文应该由共享所有的资料库，即你可以通过构造函数注入注入它：

You have two different repositories that each have a separate data context - this is the root problem - your data context should be shared by all your repositories, i.e. you can inject it via constructor injection:

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

这篇关于＆QUOT;一个实体对象不能由IEntityChangeTracker＆QUOT的多个实例被引用;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！