asp net mvc controllers - Page 388

Correct way to edit and update complex viewmodel objects using asp.net-mvc2 and entity framework

- by jslatts

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!

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