Entity Framework and MVC3 Create and Update Model

Question

So I've used EF Code First to successfully create my entities and query the database to display the items.

I now want to provide a way to edit the records.

I have a Post class which contains:

(TypeName = "varchar")]
[Required()]
public string Headline { get; set; }

public virtual PostType PostType { get; set; }

PostType is a class I wrote which has an ID and Name to categorise posts into News, Blog etc.

Now, in my Edit controller I get the post and pass this to the view in a view model. I also get a IEnumerable of the different post types.

In my view I use the below:

<div class="formFieldContainer">
    @Html.LabelFor(model => model.Post.PostType)
    @Html.DropDownListFor(model => model.Post.PostType, new SelectList(Model.PostTypes, "ID", "Name"))
    @Html.ValidationMessageFor(model => model.Post.PostType)
</div>

<div class="formFieldContainer">
    @Html.LabelFor(model => model.Post.Headline)
    @Html.EditorFor(model => model.Post.Headline)
    @Html.ValidationMessageFor(model => model.Post.Headline)
</div>

On my edit controller I have the below to handle the post:

[HttpPost, ValidateAntiForgeryToken, ValidateInput(false)]
public ActionResult Edit(int id, FormCollection collection) {
    var model = new PostViewModel();
    model.Post = _pr.GetPost(id); //gets the post from my post repository
    model.PostTypes = _ptr.GetPostTypes();

    try {
        UpdateModel(model.Post, "Post");
        _pr.Save();
        return RedirectToRoute("Posts", new { pageNumber = 0 }); //for now go to the homepage
    } catch (Exception e) {
        ModelState.AddModelError("_FORM", e.Message);
        return View(model);
    }
}

Now without the post type list and just the headline this works. However with the post type it doesn't. I get "1 is invalid" (1 being the value of the select list) which makes sense as my Post model expects a PostType object, not int.

I thought about doing something like:

model.Post.PostType = model.PostTypes.Where(x => x.ID == Int32.Parse(collection.GetValues("Post.PostType")[0])).Select(p => p).FirstOrDefault();

But 1) it doesn't work so its obviosuly not the right way and 2) since "Post.PostType" still exists, the UpdateModel fails.

Any ideas on how to do this?

What do you mean by doesn't work? Can't help without specifics. — James Hull
– James Hull, Commented Jun 4, 2011 at 17:06
Another PostType is added to the database! It should be the existing one but it's creating a new one every time. — Terry
– Terry, Commented Jun 4, 2011 at 17:06

James Hull · Accepted Answer · 2011-06-04 17:14:27Z

1

I assume your repositories _pr and _ptr are using different contexts? Entity framework must read and update from the same context. Since you are getting the post types from another context EF treats it as a new entity hence the extra row in your database.

You should share your context between repositories, session per request is a defacto best practice.

As for the update model function you can pass in a string array of properties to include in the update:

UpdateModel(model.Post, "Post", new string[] { "Headline" });

This will ignore the PostType value.

answered Jun 4, 2011 at 17:14

James Hull

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1 Comment

Terry Over a year ago

This was indeed the issue. I'll look into the session per request idea. I assume I can convert what I have done and use the Edit(Post post) idea suggested by Steve?

Steve Mallory · Accepted Answer · 2011-06-04 19:06:35Z

1

Try changing your action to take in a Post object:

public ActionResult Edit(Post post) {

With MVC 3, EF 4, the post object should be populated from the form vars, including your PostType. Then call your update and save methods.

answered Jun 4, 2011 at 19:06

Steve Mallory

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1 Comment

Terry Over a year ago

Tried it but I have the same issue. I think the reason is that I don't post a PostType back to the edit function. It's just an int from the select box, so it has no way of knowing what PostType to use.

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