更新实体，所有更改均不保存

Question

I have searched for this topic, and I realize there is a slightly related question here , and while the problem sounds very similar, the accepted solution did not work (which, if one reads the comments, one will know that the problem wasn't really solved).

Here is my problem, and I hope someone can help:

I have an Entity:

public class Garden
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual PlantHardinessZone Zone { get; set; }
}

It has a relationship with PlantHardinessZone Entity:

public class PlantHardinessZone
{
    public int Id { get; set; }
    public string Zone { get; set; }
}

In order to easily use the Zones in a DropDownListFor, I created a ViewModel:

public class GardenViewModel
{
    public int ZoneId { get; set; }
    public IEnumerable<PlantHardinessZone> Zones { get; set; }

    public Garden Garden { get; set; }
}

This ViewModel is used in several views. It currently works as expected for Creating a new Garden entity, however, Editing is not functioning correctly. If I change the Zone, it is not updated in the DB. I have stepped through the code, and the correct Zone information is returning from the View, it is just not updating. If I change the name of the Garden, that updates fine.

Here is the [HttpPost} Edit Action:

[HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult Edit(GardenViewModel viewModel)
    {
        if (ModelState.IsValid)
        {
            Garden garden = viewModel.Garden;
            garden.Zone = db.Zones.Where(z => z.Id == viewModel.ZoneId).Single();
            db.Gardens.Attach(garden); // per the solution accepted [here][2]
            db.Entry(garden).State = EntityState.Modified;
            db.SaveChanges();
            return RedirectToAction("Index");
        }
        return View(viewModel);
    }

And here is the corresponding View:

@model GardenManager.Web.ViewModels.GardenViewModel

@{
    ViewBag.Title = "Edit";
}

<h2>Edit</h2>


@using (Html.BeginForm())
{
    @Html.AntiForgeryToken()

    <div class="form-horizontal">
        <h4>Garden</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        @Html.HiddenFor(model => model.Garden.Id)

        <div class="form-group">
            @Html.LabelFor(model => model.Garden.Name, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Garden.Name, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Garden.Name, "", new { @class = "text-danger" })
            </div>
        </div>
        <div class="form-group">
            <div class="col-md-10 col-md-offset-2">
                @Html.DropDownListFor(model => model.ZoneId,
                new SelectList(Model.Zones, "Id", "Zone", Model.ZoneId),
                "Select Zone", new { @class = "form-control" })
            </div>
        </div>

        <div class="form-group">
            <div class="col-md-offset-2 col-md-10">
                <input type="submit" value="Save" class="btn btn-default" />
            </div>
        </div>
    </div>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

@section Scripts {
    @Scripts.Render("~/bundles/jqueryval")
}

Can anyone help direct me to solving this very annoying issue? All input welcome and appreciated. Thank you so much!

Answer 1

You are setting the state of Garden to Modified but that does not have any effect on the navigation properties (the link to Zone ). Thus EF will update only Garden , with no effect on the linked Zone .

If, however, you assign the Zone by it's ID , to garden.ZoneId , that will work. garden.ZoneId is a direct property of Garden and it will get everything properly linked.

garden.ZoneId = db.Zones.Where(z => z.Id == viewModel.ZoneId).Single().Id;

To recapitulate:
- garden.Zone is not a true property of the object, it's just a link handled behind the scenes by EF. This is why it fails updating.
- garden.ZoneId is a true property of the object, thus it get's updated properly if you change it.

db.Gardens.Attach(garden); attaches only the garden object. It doesn't attach the other objects that might be linked to it.

Additionally I would recommend to first attach the entity to the context and then change it's properties and state.