错误地更新多对多连接表

Question

我有一个 ChangeRequest 对象和一个具有多对多关系的 BusinessArea 对象。有一个连接表：ChangeRequestBusinessArea。

如果我使用 BusinessAreaID 2、7、8 和 10 创建并保存新的 ChangeRequest，则连接表会更新得很好。

例如

ChangeRequestID BusinessAreaID
1               2
1               7
1               8
1               10

但是，当我随后编辑并保存 BusinessAreaID 为 1、2、3、7 和 10 的相同 ChangeRequest 时，我得到以下信息：

ChangeRequestID BusinessAreaID
1               2
1               7
1               8
1               10
1               11
1               12
1               13
1               14
1               15

代码如下：

类

namespace MOC.Models
{
public class ChangeRequest
{
    public ChangeRequest()
    {
        BusinessAreas = new List<BusinessArea>();
    }

    public int ChangeRequestID { get; set; }
    public string ChangeRequestName { get; set; }

    public virtual ICollection<BusinessArea> BusinessAreas { get; set; }
}
}

namespace MOC.Models
{
public class BusinessArea
{
    public int BusinessAreaID { get; set; }
    public string BusinessAreaName { get; set; }

    public virtual ICollection<ChangeRequest> ChangeRequests { get; set; }
}
}

动作方法

[HttpPost]
public ActionResult Edit(int id, ChangeRequestViewModel ChangeRequestViewModel)
{
    if (ModelState.IsValid)
    {
        var changeRequest = new ChangeRequest
        {
            ChangeRequestID = id
        };

        AddOrUpdateBusinessAreas(changeRequest, ChangeRequestViewModel.BusinessAreas);
        db.Entry(changeRequest).State = EntityState.Modified;
        db.SaveChangeRequests();

        return RedirectToAction("Index");
        }
        return View(ChangeRequestViewModel);
    }

    private void AddOrUpdateBusinessAreas(ChangeRequest ChangeRequest, IEnumerable<AssignedBusinessAreaData> assignedBusinessAreas)
    {
        foreach (var assignedBusinessArea in assignedBusinessAreas)
        {
            if (assignedBusArea.Assigned) {
                var busarea = new BusArea { BusAreaID = assignedBusArea.BusAreaID };
                Change.BusAreas.Add(busarea);
            } else {
                var busarea = new BusArea { BusAreaID = assignedBusArea.BusAreaID };
                Change.BusAreas.Remove(busarea);
            }
        }
    }

Answer 1

您必须从数据库中加载ChangeRequest包括当前与其相关的BusinessAreas，以便能够删除关系。

我假设ChangeRequestViewModel.AssignedBusinessAreaData 包含带有标志Assigned 的所有可能区域，如果该区域是否必须分配给ChangeRequest。那么您的操作方法可能类似于以下内容：

[HttpPost]
public ActionResult Edit(int id, ChangeRequestViewModel ChangeRequestViewModel)
{
    if (ModelState.IsValid)
    {
        var changeRequest = db.ChangeRequests
            .Include(c => c.BusinessAreas) // Important !
            .Single(c => c.ChangeRequestID == id);

        foreach (var assignedBusArea in ChangeRequestViewModel.BusinessAreas)
        {
            if (assignedBusArea.Assigned)
            {
                if (!changeRequest.BusinessAreas
                    .Any(b => b.BusinessAreaID == assignedBusArea.BusAreaID))
                {
                    var busArea = new BusinessArea
                    {
                        BusAreaID = assignedBusArea.BusAreaID
                    };
                    db.BusinessAreas.Attach(busArea);
                    // Attach is important to avoid duplication of the area
                    changeRequest.BusinessAreas.Add(busArea);
                }
                // else do nothing if the assigned area
                // already belongs to the changeRequest
            }
            else
            {
                var busArea = changeRequest.BusinessAreas.SingleOrDefault(
                    b => b.BusinessAreaID == assignedBusArea.BusAreaID);
                if (busArea != null)
                    changeRequest.BusinessAreas.Remove(busArea);
                // else do nothing if the unassigned area
                // does not belong to the changeRequest anyway
            }
        }
        db.SaveChanges();

        return RedirectToAction("Index");
    }            

    return View(ChangeRequestViewModel);
}