asp.net mvc custom model binding in an update entity scenario

Question

Hi I have a question about model binding. Imagine you have an existing database entity displayed in a form and you'd like to edit some details, some properties eg createddate etc are not bound to the form, during model binding, these properties are not assigned to the model as they are not on the http post data or querystrong etc, hence their properties are null. In my controller method for update , Id just like to do

public ActionResult Update( Entity ent) { //Save changes to db }

but as some properties are null in ent, they override the existing database fields which are not part of the form post data, What is the correct way to handle this? Ive tried hidden fields to hold the data, but model binding does not seem to assign hidden fields to the model. Any suggestions would be appreciated

Answer 1

You shouldn't be sending your entity to your view, you should send a slim version of it called a DTO (data transfer object) or ViewModel.

Only send the properties to the view (and hence the form that gets posted back) that you want the user to update with that action.

In your POST handler you can then validate and copy the properties across to your entity.

an AutoMapper can help if you have lots of properties

something like:

public class User
{
    int id;
    string name;
    string email;
}

public class EditUserEmailDto
{
    string email;
}

// get
public ActionResult EditEmail(int id,)
{
    return View("EditEmail", new EditUserEmailDto());
}    

// post
public ActionResult EditEmail(int id, EditUserEmailDto dto)
{
    if(!ModelState.IsValid)
        return View("EditEmail", dto);

    var user = userRepo.Get(id);
    user.email = dto.email;
    userRepo.Save(user);

    return;
}