Question: I am using Entity Framework 1 with .net 3.5.

I am doing something simple like this:

```
var roomDetails = context.Rooms.ToList();

foreach (var room in roomDetails)
{        
   room.LastUpdated = DateTime.Now;
}

```

I am getting this error when I try to do:

```
 context.SaveChanges();

```

I get the error:

> 
> **Unable to update the EntitySet - because it has a DefiningQuery and no <UpdateFunction> element exists in the <ModificationFunctionMapping> element to support the current operation.**
> 
> 
> 

I am doing lots of updates on the context and not having any issues, it's only when I try to update this particular entity.

All my searching shows up the same thing, that there is no primary key declared on the entity that I'm trying to update. But alas, I do have a Primary key declared...

Answer: 
It usually happens because one of the following reasons:

* Entity Set is mapped from Database view
* A custom Database query
* Database table doesn't have a primary key

After doing so, you may still need to update in the Entity Framework designer (or alternatively delete the entity and then add it) before you stop getting the error.
Set Primary Key then save Table and Refresh then go to Model.edmx delete Table and get again .