C# 从MVC保存类之间的关联时出现实体框架错误

我们将MVC与实体框架结合使用。 在某种程度上，我们正试图在两个实体之间建立联系。这在单元测试中可以正常工作，但从MVC控制器方法尝试时会出现以下错误：

“保存不公开外部数据的实体时出错 关系的键属性。EntityEntries属性 将返回null，因为无法将单个实体标识为 异常的来源。可以在保存时处理异常 通过在实体类型中公开外键属性使其更容易。”

（精简）类别：

通过的单元测试：

    [TestMethod]
public void LinkOrganizationToPositionTest()
{
    // arrange
    DbModel dbModel;
    Organization org;
    Position pos;
    Guid orgId;

    using (dbModel = new DbModel())
    {
        dbModel.Database.Delete();
        dbModel.Database.Create();

        // - first organization
        org = dbModel.Organizations.Create();
        org.Name = "TestOrgFirst";
        dbModel.Entry(org).State = EntityState.Added;

        pos = dbModel.Positions.Create();
        pos.Function = "TestFunc";
        dbModel.Entry(pos).State = EntityState.Added;

        // - link pos to first org
        pos.Organization = org;

        org = dbModel.Organizations.Create();
        org.Name = "TestOrgSecond";
        dbModel.Entry(org).State = EntityState.Added;
        orgId = org.Id;
        dbModel.SaveChanges();
    }

    // act
    // - obtain "fresh" model
    using (dbModel = new DbModel())
    {
        // - get second org
        org = dbModel.Organizations.Find(orgId);
        pos = dbModel.Positions.Find(pos.Id);
        pos.Organization = org;
        dbModel.SaveChanges();
    }

    // assert
    using (dbModel = new DbModel())
    {
        Position actual =
            dbModel.Positions
                .Include("Organization")
                    .First(x => x.Id.Equals(pos.Id));
        // - link was saved 
        Assert.AreEqual(
            "TestOrgSecond", 
            actual.Organization.Name
            );
    }
}

为什么MVC需要OrganizationId外键属性？

---

是否有一个简单的修复程序不需要模型中的所有外键？

我可以衷心建议显式实现外键。它让生活变得更简单！只是好奇。你是否尝试过将职位添加到组织的联系人中？@ilmatte:是的，我甚至尝试过在Organi中向集合添加职位组织的组织化和设置Position@Dabblernl：我可以这样看，但这比丑陋更糟糕：OO实现不应该需要关系外键。@kc了解外键关联与独立关联（没有原始FK属性）的优势。无论从哪个角度看，EF类模型仍然是DAL，因此请针对其主要职责对其进行优化。您已经有了主键、基类

实体
、嵌套映射类。原始FKs不会让它变得更“糟糕”：
    [HttpPost]
public ActionResult Edit(Position position, string organizationId = "")
{
    if (!ModelState.IsValid)
    {
        return View(position);
    }
    db.Entry(position).State = EntityState.Modified;
    if (!string.IsNullOrEmpty(organizationId))
    {
        Guid orgId = Guid.Parse(organizationId);
        Organization organization =
            db.Organizations
                .First(x => x.Id.Equals(orgId));
        position.Organization = organization;
    }
    db.SaveChanges();
    RedirectToAction("Index");
}

    [TestMethod]
public void LinkOrganizationToPositionTest()
{
    // arrange
    DbModel dbModel;
    Organization org;
    Position pos;
    Guid orgId;

    using (dbModel = new DbModel())
    {
        dbModel.Database.Delete();
        dbModel.Database.Create();

        // - first organization
        org = dbModel.Organizations.Create();
        org.Name = "TestOrgFirst";
        dbModel.Entry(org).State = EntityState.Added;

        pos = dbModel.Positions.Create();
        pos.Function = "TestFunc";
        dbModel.Entry(pos).State = EntityState.Added;

        // - link pos to first org
        pos.Organization = org;

        org = dbModel.Organizations.Create();
        org.Name = "TestOrgSecond";
        dbModel.Entry(org).State = EntityState.Added;
        orgId = org.Id;
        dbModel.SaveChanges();
    }

    // act
    // - obtain "fresh" model
    using (dbModel = new DbModel())
    {
        // - get second org
        org = dbModel.Organizations.Find(orgId);
        pos = dbModel.Positions.Find(pos.Id);
        pos.Organization = org;
        dbModel.SaveChanges();
    }

    // assert
    using (dbModel = new DbModel())
    {
        Position actual =
            dbModel.Positions
                .Include("Organization")
                    .First(x => x.Id.Equals(pos.Id));
        // - link was saved 
        Assert.AreEqual(
            "TestOrgSecond", 
            actual.Organization.Name
            );
    }
}