Receiving an attempt was made to remove a relationship between x and x however one of the relationship's foreign keys - asp.net-mvc-3

Question

I have an MVC project and I have a case where i need to update a parent and multiple child entities at the same time. In the post action I am receiving "an attempt was made to remove a relationship between x and x however one of the relationship's foreign keys" which is strange, all I'm doing is update, I'm not droping any entity whatsoever. I am using Linq to SQL and MVC3. The pseudocode is like the following:
#model Project.Models.ParentModel
...
#using (Html.BeginForm()) {
#Html.Label("Parent property")
#Html.EditorFor(model => model.ParentProperty)
#foreach (var child in Model.Childs)
{
Html.RenderPartial("_EditChild", child)
// Which is nothing more than a label and an editor for a property like:
// #model Project.Models.ChildModel
// #Html.Label("Child property")
// #Hteml.EditorFor(model => model.ChildProperty)
}
...
}
The Action looks like:
public ActionResult Edit(int id, FormCollection collection)
{
var parent = new Parent();
TryUpdateModel(Parent()); // which updates the parent and the child properties correctly
dataContext.SubmitChanges();
}
Can anybody explaing this behavior. Once again, I'm not removing or dropping any child entities!

Answer 1

The binding over a list can be pretty nasty, I had some problems with it myself. I modified my list editing code to work with childs and tested it, it worked and the data is correctly bound and visible in the post action:
#model MvcApplication2.Models.Parent
#using (Html.BeginForm())
{
<table>
#{
<tr>
<td>
#Html.TextBoxFor(m => m.Text)
#Html.HiddenFor(m => m.ID)
</td>
</tr>
for (int i = 0; i < Model.Children.Count; i++)
{
<tr>
<td>
#Html.TextBoxFor(x => x.Children[i].Title)
#Html.HiddenFor(x => x.Children[i].ID)
</td>
</tr>
}
}
</table>
<div class="button">
<input class="submit" type="submit" name="btnSave" id="btnSave" value="Save" />
</div>
}
Controller for my test looks like this:
[HttpGet]
public ActionResult EditingChildren()
{
Parent parent = new Parent() { Text = "" };
parent.Children = new List<Child>();
parent.Children.Add(new Child() { Title = "" });
parent.Children.Add(new Child() { Title = "" });
parent.Children.Add(new Child() { Title = "" });
return View(parent);
}
[HttpPost]
public ActionResult EditingChildren(Parent parent)
{
// save parent with children
}
Editing my post about saving data back with linq to sql:
If you are not binding the ID on the view, it will be left empty in the object in the post method. That gives you troubles saving back the data.
I usally bind therefore the ID to an hidden field so it will not be empty any more (view code above edited and added HiddenFor beneath TextBoxFor).
Have also a look about updating data with linq to sql on this website:
http://davedewinter.com/2009/04/07/linq-to-sql-updating-entities/ (under Attach an Entity, Change Properties, Update)
and this post:
enter link description here