I have a table in my database with a one to many relationship to another table:
ParentObject
ID
Name
Description
ChildObject
ID
Name
Description
ParentObjectID
AnotherObjectID
The objects are mapped into
Entity Framework and exposed through a
data access class.
It seemed like ViewModels are recommended when the
data to be displayed greatly differs from the domain object, so I created a ViewModel as follows:
public class ViewModel {
public IList<ParentObject> ParentObjects { get; set; }
public ParentObject selectedObject { get; set; }
public IList<ChildObject> ChildObjects { get; set; }
}
I have a view that displays a list of ParentObjects and when clicked will allow a ChildObject to be modified saved.
<% using (Html.BeginForm()) { %>
<table>
<% foreach (var parent in
Model.ParentObjects) { %>
<tr>
<td>
ObjectID [<%= Html.Encode(parent.ID)%>]
</td>
<td>
<%= Html.Encode(parent.Name)%>
</td>
<td>
<%= Html.Encode(parent.Description)%>
</td>
</tr>
<% } %>
</table>
<% if (Model.ParentObject != null) { %>
<div>
Name:<br />
<%= Html.TextBoxFor(model =>
model.ParentObject.Name) %>
<%= Html.ValidationMessageFor(model =>
model.ParentObject.Name, "*")%>
</div>
<div>
Description:<br />
<%= Html.TextBoxFor(model =>
model.ParentObject.Description) %>
<%= Html.ValidationMessageFor(model =>
model.ParentObject.Description, "*")%>
</div>
<div>
Child Objects
</div>
<% for (int i = 0; i <
Model.ParentObject.ChildObjects.Count(); i++) { %>
<div>
<%= Html.DisplayTextFor(sd => sd.ChildObjects[i].Name) %>
</div>
<div>
<%= Html.HiddenFor(sd => sd.ChildObjects[i].ID )%>
<%= Html.TextBoxFor( sd => sd.ChildObjects[i].Description) %>
<%= Html.ValidationMessageFor(sd => sd.ChildObjects[i].Description, "*") %>
</div>
<% }
}
} %>
This all works fine. My question is around the best way to update the EF objects and persist the changes back to the database. I initially tried:
[HttpPost]
public ActionResult Edit(ViewModel viewModel) {
ParentObject parent = myRepository.GetParentObjectByID(viewModel.SelectedObject.ID);
if ((!ModelState.IsValid)
|| !TryUpdateModel(parent, "SelectedObject", new[] { "Name", "Description" })) {
|| !TryUpdateModel(parent.ChildObjects, "ChildObjects", new[] { "Name", "Description" })) {
//Code to handle failure and return the current
model snipped
return View(viewModel);
}
myRepository.Save();
return RedirectToAction("Edit");
}
When I try to save a change to the child object, I get this exception: Entities in 'MyEntities.ChildObject' participate in the 'FK_ChildObject_AnotherObject' relationship. 0 related 'AnotherObject' were found. 1 'AnotherObject' is expected.
Investigation on StackOverflow and generally googling led me to this blog post that seems to describe my problem: TryUpdateModel() does not correctly handle nested collections. Apparently, (and stepping through the debugger confirms this) it creates a new ChildObject instead of associating with the EF objects from my instantiated context.
My hacky work around is this:
if (viewModel.ChildObjects.Count > 0) {
foreach (ChildObject modelChildObject in viewModel.ChildObjects) {
ChildObject childToUpdate = ParentObject.ChildObject.Where(a => a.ID == modelChildObject.ID).First();
childToUpdate.Name = modelChildObject.Name;
}
}
This seems to work fine. My question to you good folks: Is there correct way to do this? I tried following the suggestion for making a custom
model binder per the blog link I posted above but it didn't work (there was an issue with reflection) and I needed to get something going ASAP.
PS - I tried to cleanup the code to hide specific information, so beware I may have hosed something up. I mainly just want to know if other people have solved this problem.
Thanks!
