Could not assemble any primary key columns for mapped table

It then adds columns to the DataColumnCollection of the DataTable, and configures the following DataColumn properties if they exist at the data source:ДЄutoIncrement. If the connection is open before FillSchema is called, it remains open.ДЄ FillSchema operation adds a DataTable to the destination DataSet. If the connection is closed before FillSchema is called, it is opened to retrieve data, then closed. The connection object associated with the SelectCommand must be valid, but it does not need to be open. The FillSchema method retrieves the schema from the data source using the SelectCommand. Returns DataTableДЄn array of DataTable objects that contain schema information returned from the data source. In this article Overloads FillSchema(DataSet, SchemaType, IDbCommand, String, CommandBehavior)ДЄdds a DataTable to the specified DataSet and configures the schema to match that in the data source based on the specified SchemaType.ДЇillSchema(DataTable, SchemaType, IDbCommand, CommandBehavior)Д¬onfigures the schema of the specified DataTable based on the specified SchemaType, command string, and CommandBehavior values.ДЄdds a DataTable to the specified DataSet and configures the schema to match that in the data source based upon the specified SchemaType and DataTable.Д¬onfigures the schema of the specified DataTable based on the specified SchemaType.ДЄdds a DataTable named 'Table' to the specified DataSet and configures the schema to match that in the data source based on the specified SchemaType. Adds a DataTable to a DataSet and configures the schema to match that in the data source.

Could not assemble any primary key columns for mapped table