对象状态管理器错误

Question

我有控制器发布操作

public ActionResult Demographics(string submitButton, DemographicsViewModel model)
{
    switch (submitButton)
    {
        case "Home":
            return RedirectToAction("Index");
        case "Next Page":
            using (ProposalRepository proposalRepository = new ProposalRepository())
            {
                model.Proposal.UserID = proposalRepository.GetUserByName(MasterHelper.CurrentUsername).UserID;
                model.Proposal.CustomerID = proposalRepository.GetCustomerByName(model.CustomerName).CustomerID;

                if (model.Proposal.ProposalID != 0)
                {
                    proposalRepository.Update(model.Proposal);
                }
                else
                {
                    proposalRepository.AddProposal(model.Proposal);
                }

                proposalRepository.SaveChanges();
            }

            return RedirectToAction("GRQuestions", model.Proposal);
        default:
            return View();
    }
}

当我尝试更新时

public void Update(Proposal proposal)
{
    mContext.Proposals.ApplyCurrentValues(proposal);
}

抛出错误：在 ObjectStateManager 中找不到具有与所提供对象的键匹配的键的对象。验证所提供对象的键值是否与必须应用更改的对象的键值匹配。 我正在寻找解决方案，我发现了这个：

public ActionResult Demographics(string submitButton, DemographicsViewModel model)
{
    switch (submitButton)
    {
        case "Home":
            return RedirectToAction("Index");
        case "Next Page":
            using (ProposalRepository proposalRepository = new ProposalRepository())
            {
                Proposal proposal = proposalRepository.GetById(model.Proposal.ProposalID);

                model.Proposal.UserID = proposalRepository.GetUserByName(MasterHelper.CurrentUsername).UserID;
                model.Proposal.CustomerID = proposalRepository.GetCustomerByName(model.CustomerName).CustomerID;

                if (model.Proposal.ProposalID != 0)
                {
                    proposalRepository.Update(model.Proposal);
                }
                else
                {
                    proposalRepository.AddProposal(model.Proposal);
                }

                proposalRepository.SaveChanges();
            }

            return RedirectToAction("GRQuestions", model.Proposal);
        default:
            return View();
    }
}

只添加一行：

Proposal proposal = proposalRepository.GetById(model.Proposal.ProposalID);

效果很好，但我认为这是一个愚蠢的决定，我相信有更好的方法和解释？？？

Answer 1

ApplyCurrentValues 就是这样工作的。您必须先加载实体才能使用它（= 在修改附加实体时使用它）。如果您不想先加载它，请将您的Update 方法更改为：

public void Update(Proposal proposal)
{
    mContext.Proposals.Attach(proposal);
    mContext.ObjectStateManager.ChangeObjectState(proposal, EntityState.Modified);
}