Query #1: The documentation says to add the .QueryString property to indicate the name of the master's ID field. However, it makes no mention of setting .ForeignKey to the field name in the child datasource.
We suspect that you are mentioning about the ForeignKeyField property of the Child Grid which is used when the mapping field name differs in the parent and child table. Considering this, we have created an improvement task to include the details on this property. It will be refreshed online as early as possible.
Query #2: how do I populate the foreign key field so that it will show up in the child grid properly
We suggest you to define the foreign key column of the child grid to get the corresponding details while editing and saving. We can set the visible property of the corresponding column as “false” if we don’t want the column to be displayed in grid.
Even if the visible property is set as false, the corresponding column values will be obtained in the argument when updating the record.
Ragavee U S.