According to MSDN :
"You can hide the primary key, like any other column, using the Scaffold attribute and setting its value to false. Since the automatically generated keys are not recognized, insert page templates do not work with EDM by default for tables that have automatic primary keys, unless you create a partial class for the object and apply the Scaffold attribute with the value false. "
In addition, as a third-party option, it is preferable to use "newsequentialid ()" for the default Guid if you are using SQL Server 2005 or higher, since it is more efficient to insert.
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