How Do I: Create a One-to-Many Data Entry Form?
Pay real close attention to where the many dataset is selected from. Note that the order detail below the Orders, if used will be filtered on the order selected.
When filtering the second combo box on the first, be sure to select the correct binding source from the smart tag Data source combo box. If set up correctly the second combo box will be automatically filtered on the first.
The order in which the datasets are filled by the table adapters is important.
The order in which the tables are updated is important.
The above procedure works well for details but not datagrid view. For the datagrid view combos, use a datagrid view with a filter to display master - details.