There is a property named "PrimaryKey". I have this property always null. How can be this property set ?

It can't - Typed Lists are read only. Is this property coming from an existing table - ie, do you have a column actually called "PrimaryKey" ? And is it a primary key on the table ?

Matt

No this property is part of the base class DataTable. So this property cannot be set ? Its just a needless property from DataTable ?

Sorry. my misunderstanding. Yes, it's a hangover from the fact that TypedLists inherit from DataTables. Because DataTables can also be used to represent single tables, they need a property to set and read the PrimaryKey columns. It can be safely ignored for your purposes.

http://msdn.microsoft.com/en-us/library/system.data.datatable.primarykey.aspx

Matt