Question

我有三张表如下：

public class A {
    public int A_ID {get;set;}
    ...
}

public class B {
    public int B_ID {get;set;}
    ...
}

public class C {
    public int A_ID {get;set;}
    public int C_B_ID {get;set;}
    ...

    public virtual A a {get;set;}
    public virtual B b {get;set;}
}

我设置了以下按键：

modelBuilder.Entity<C>()
                    .HasRequired(x => x.a)
                    .WithMany()
                    .HasForeignKey(u => u.A_ID);

modelBuilder.Entity<C>()
                    .HasRequired(x => x.b)
                    .WithMany()
                    .HasForeignKey(u => u.C_B_ID);

modelBuilder.Entity<C>()
             .Property(t => t.A_ID)
                .HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);

在“创建视图”页面上，我有以下外键的下拉列表：

<div class="editor-label">
    @Html.LabelFor(model => model.A_ID, "A")
</div>
<div class="editor-field">
    @Html.DropDownList("A_ID", String.Empty)
    @Html.ValidationMessageFor(model => model.A_ID)
</div>

<div class="editor-label">
    @Html.LabelFor(model => model.C_B_ID, "B")
</div>
<div class="editor-field">
    @Html.DropDownList("C_B_ID", String.Empty)
    @Html.ValidationMessageFor(model => model.C_B_ID)
</div>

这是我的创建功能：

//
    // GET: /C/Create

    public ActionResult Create()
    {
        ViewBag.A_ID = new SelectList(db.As, "A_ID", "Name");
        ViewBag.B_ID = new SelectList(db.Bs, "B_ID", "Name");
        return View();
    }
//
//POST

public ActionResult Create(C c_instance)
    {
        if (ModelState.IsValid)
        {
            db.Cs.Add(c_instance);
            db.SaveChanges();
            return RedirectToAction("Index");
        }

        ViewBag.A_ID = new SelectList(db.As, "A_ID", "Name", c_instance.A_ID);
       ****EDITED***  ViewBag.B_ID = new SelectList(db.Bs, "B_ID", "Name", c_instance.C_B_ID);
        return View(c_instance);
    }

现在，在create函数中，我收到在A_ID的第一个下拉列表中选择的值，但C_B_ID的下拉值始终为零。这导致了这个问题：

The INSERT statement conflicted with the FOREIGN KEY constraint
"FK_dbo.Cs_dbo.Bs_C_B_ID". 
The conflict occurred in database "C:\temp.MDF", table "dbo.Bs", column 'B_ID'.
The statement has been terminated.

现在，这种情况正在发生，因为C_instance.A_ID具有从下拉列表中选择的正确A_ID，但始终是C_instance.C_B_ID = 0！（并且下拉列表会显示表B中的所有条目，我选择其中一个）

导致这种情况的原因是什么？

Answer 1

您需要将列表传递给DropDownList帮助程序。

@Html.DropDownList("A_ID", ViewBag.A_ID, String.Empty)
@Html.DropDownList("C_B_ID", ViewBag.B_ID, String.Empty)

外键的DropDownList不会将值返回给Create Function

1 个答案: