Question

For some time I couldn’t find out the cause of an error when trying to update a field in a table using WCF Data Services plus Entity Framework:

MydbEntities context = new MydbEntities(new Uri("http://localhost:53051/Services/MydbService.svc"));
MyEntity entitytoedit = context.MyEntity.FirstOrDefault();
entitytoedit.Name = "TheNewName";
context.UpdateObject(entitytoedit);
context.BeginSaveChanges(OnChangesSaved, context);
...

The error was like following: RequestException An error occurred while processing this request.

The fix was to add an autoincremental decimal(18, 0) field as the Primary Key with Identity Specification IsIdentity = yes instead of just a varchar(20) field as the Primary Key.

Please, could anybody explain the nature of the problem: should I always use autoincremental Primary Keys with WCF Data Services? If not, where in fact am I wrong?

Answer 1

I think it is more Entity Framework question than WCF Data Services.

You can either have primary key field that you set by hands and you must set StoreGeneratedPattern to None.

Or you can use AutoIncrement field as primary key and in this case you must set StoreGeneratedPattern for it to Identity.

Mixing this to cases always break the things. In addition when you do Model First, primary key field by default has type int and StoreGeneratedPattern set to Identity, so just changing the type to decimal as in your case is not enough.