While working with SQL Server and Entity Framework the following error was raised after adding a new table into the SQL Database and updating the model in my project from the DB:

"Unable to update the EntitySet 'Customers' because it has a DefiningQuery and no <InsertFunction> element exists in the <ModificationFunctionMapping> element to support the current operation."

The error was raised as an exception on calling the SaveChanges method on the context after adding a new record into a list/ table on the database.

The solution to the problem was simple – although my new SQL table had an ID column, I hadn’t set the column as the primary key. Setting the column as a primary key in SQL Server Management Studio then going back to my Visual Studio project and rebuilding the entity model from the database made the error go away and let me successfully save new records to the table.