DropDownList value insert in database as foreign key

Question

I am trying to insert a categoryID to the table Post, but my code is creating a new category instead of using the selected value from the dropdownlist.

I am starting to study ASP.NET MVC, so I don't know how I can solve this. I can get the real value from dropdownlist but when the insert query runs it insert a new category and attribute her to post insert.

public ActionResult Create([Bind(Include = "PostID,Text,CategoryID")] Posts posts)
{
    if (ModelState.IsValid)
    {
        int CategoryID = Convert.ToInt32(Request["CategoryID"]);
        posts.Category = new Categories { CategoryID = CategoryID };
        db.Posts.Add(posts);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    return View(posts);
}

public ActionResult Create()
{
    ViewBag.CategoryID = new SelectList(db.Categories, "CategoryID", "Name");
    return View();
}

View Code:

   <h2>Create</h2>


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

    <div class="form-horizontal">
        <h4>Posts</h4>
        <hr />
        @Html.ValidationSummary(true, "", new { @class = "text-danger" })
        <div class="form-group">
            @Html.LabelFor(model => model.Text, htmlAttributes: new { @class = "control-label col-md-2" })
            <div class="col-md-10">
                @Html.EditorFor(model => model.Text, new { htmlAttributes = new { @class = "form-control" } })
                @Html.ValidationMessageFor(model => model.Text, "", new { @class = "text-danger" })

                Categoria:<br />
                @Html.DropDownList("CategoryID", "Selecione uma categoria")
            </div>
        </div>

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

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

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

Post Model:

 public class Post
{
    [Key]
    public int PostID { get; set; } /*PRIMARY KEY*/
    public string Text { get; set; }

    public virtual Categories Category { get; set;} /*ONE POST HAS ONLY ONE CATEGORY*/ //

}

It's because this is an 'Insert', it will simply just insert. You have no checks against it. If you want to update values, you can update — JamesS, Jan 09 '19 at 16:55

Max · Answer 1 · 2019-01-10T15:34:08.863

Let's suppose that you have two entities Post and Category, where Category can have many Posts, i.e. entity Post has property CategoryId. Then when you build a new Post entity for insert/update you need to set CategoryId, i.e.

post.CategoryId = your_value_from_dropdown;

or you can get needed Category by CategoryID, for example,

var category = db.Category.Where(x => x.CategoryId == your_value_from_dropdown).FirstOrDefault();

and set this category for post through the navigation property like post.Category = category and then make insert or update for post.

TanvirArjel · Accepted Answer · 2019-01-10T15:09:19.980

0

First write your Post model class as follows:

public class Post
{
    [Key]
    public int PostId {get; set;}

    public string Text {get; set;}

    [ForeignKey("Category")]
    public int CategoryID {get; set;}

    public Category Category {get; set;}
}

Looking at your Create post method it seems that problem is the following two lines:

int CategoryID = Convert.ToInt32(Request["CategoryID"]);
posts.Category = new Categories { CategoryID = CategoryID };

Remove these two lines of code! you don't need to assign Category to Post creating a new Category with the CategoryId coming with Post. Keep your Create post method as simple as follows and it should work fine.

public ActionResult Create([Bind(Include = "PostID,Text,CategoryID")] Posts posts)
{
    if (ModelState.IsValid)
    {
        db.Posts.Add(posts);
        db.SaveChanges();
        return RedirectToAction("Index");
    }

    return View(posts);
}

edited Jan 10 '19 at 15:09

answered Jan 10 '19 at 03:18

TanvirArjel

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Is not working, I got **null** in categoryID on table posts – JNeves Jan 10 '19 at 12:37
Are you posting single or multiple post from view? – TanvirArjel Jan 10 '19 at 12:39
Great! Share your Razor View code (Post Create Form) to the question! This will help to identify the problem! – TanvirArjel Jan 10 '19 at 12:40
The answer was that I needed a linq query to get the object from ID to associate that value to **posts.Category** but I'm not good enough on linq and entity requires that knowledge – JNeves Jan 10 '19 at 13:28
I have seen the solution! But this is not the good! way! Your are missing something! You have to pass it from view! You don't need to access database every time for it! – TanvirArjel Jan 10 '19 at 13:30
I wanted to add your view code? but you didn't! then how will understand your problem! – TanvirArjel Jan 10 '19 at 13:31
Already edited with my view code. Sorry I don't understood it was a bad way to make things happen – JNeves Jan 10 '19 at 14:38
Thanks! Now does not your `Posts posts` on the create post method contain any value for `CategoryID` while you submitting the form? – TanvirArjel Jan 10 '19 at 14:40
Yes the default value is null – JNeves Jan 10 '19 at 14:41
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/186488/discussion-between-tanvirarjel-and-jneves). – TanvirArjel Jan 10 '19 at 14:42
@JNeves check the chat please! – TanvirArjel Jan 10 '19 at 15:12

DropDownList value insert in database as foreign key

2 Answers2