>>Another alternative (maybe better) would be an ActionFilterAttribute which could be added to applicable methods :
>>
>>https://msdn.microsoft.com/en-us/library/system.web.http.filters.actionfilterattribute%28v=vs.118%29.aspx
>
>Do you have samples, Viv?
>
>I found this
>
>http://www.asp.net/mvc/overview/older-versions-1/controllers-and-routing/understanding-action-filters-cs
>
>but I don't understand how to access the model's properties in that filter.
>
>Say, this is my Update method in the controller (quite complicated in this particular case)
>
>

>[Route("")]
>        [HttpPut]
>        public IHttpActionResult UpdateAccount(EditAccountViewModel accountViewModel)
>        {
>            // Update Contacts
>            _contactsAdapter.UpdateContactsAndChildren(accountViewModel.ContactPerson);
>
>            Accounts account = AutoMapper.Mapper.Map<EditAccountViewModel, Accounts>(accountViewModel);
>            // The web page assigns false/true or 0/1, converting here.
>		    if (account.WebITtype == 0)
>		    {
>		        account.WebITtype = 2;
>		    }
>		    else
>		    {
>		        account.WebITtype = 1;
>		    }
>            List<DualListViewModel> currentSecAcct = (from secAcct in _secAcctAdapter.GetAll()
>                                                      join secRoles in _secRoleAdapter.GetAllRoles()
>                                                      on secAcct.RoleNo equals secRoles.RoleNo
>                                                      where secAcct.AcctName == accountViewModel.AcctName
>                                                      select new DualListViewModel
>                                                      {
>                                                          Descrip = secRoles.Descrip,
>                                                          ItemId = secAcct.PriKey
>                                                      }).ToList();
>
>            if (accountViewModel.AssignedRoles.Any())
>            {
>                if (currentSecAcct.Any())
>                {
>                    List<DualListViewModel> newSecRoles = accountViewModel.AssignedRoles.Except(currentSecAcct.AsEnumerable()).ToList();
>                    List<DualListViewModel> removedSecRoles = currentSecAcct.Except(accountViewModel.AssignedRoles.AsEnumerable()).ToList();
>                    foreach (var role in newSecRoles)
>                    {
>                        SecAcct secAcct = new SecAcct();
>                        secAcct.RoleNo = role.ItemId;
>                        secAcct.AcctName = accountViewModel.AcctName;
>                        _secAcctAdapter.Add(secAcct);
>                    }
>
>                    foreach (var role in removedSecRoles)
>                    {
>                        _secAcctAdapter.Delete(role.ItemId);
>                    }
>                }
>                else
>                {
>                    foreach (var role in accountViewModel.AssignedRoles)
>                    {
>                        SecAcct secAcct = new SecAcct();
>                        secAcct.RoleNo = role.ItemId;
>                        secAcct.AcctName = accountViewModel.AcctName;
>                        _secAcctAdapter.Add(secAcct);
>                    }
>                }
>            }
>            else if (currentSecAcct.Any())
>            {
>                foreach (var roles in currentSecAcct)
>                {
>                    _secAcctAdapter.Delete(roles.ItemId);
>                }
>            }
>
>            SetOperatorAndSalespoint(account);
>            // Update contactId
>            var contatId = accountViewModel.ContactPerson.ContactId;
>            account.ContactId = contatId;
>
>            _accountsAdapter.Update(account);
>            
>            accountViewModel = AutoMapper.Mapper.Map<Accounts, EditAccountViewModel>(account);
>
>            // Update contact with latest information
>            accountViewModel.ContactPerson = _contactsAdapter.GetContactsAndChildrenById(contatId);
>
>            return Ok(accountViewModel);
>        }

>
>The SetOperatorAndSalespoint(account) is what I'd like to make a filter if I am going to go with the filter route. But the question is - how from the filter I can access the accountViewModel (any view model) and set the properties of it (and these properties are only in a few of the models, not in every model).
>
>So, I still don't understand what I am supposed to do here, although filter's approach looks interesting.
>
>I was also thinking of the simplest approach (for me). Create a new layer ViewModel class based on our abstract BaseEditViewModel class. This class will have these extra properties (Salespoint, Operator, DateTime, ModSp, ModOp). Have methods to update these properties. Re-point models that will have these properties to that class instead of just the BaseEditViewModel class. And then just call the method of this new class in the Save method.
>
>This approach looks the simplest to me and I would know how to implement it. Do you think it's an OK route to take with the extra layer class? I think having extra properties in the ViewModel even if they are not used in the model class is OK and should not be a problem.
>
>Thanks again.
>
>UPDATE. Found this http://stackoverflow.com/questions/872796/asp-net-mvc-accessing-view-model-from-a-custom-action-filter which may be a way to go.

I've only used the approach with WebAPI rather than the MVC model but they are substantially the same. Looks like that might work.