So - if your dropdowns are in a repeating section, it is probably best to just query for all the data (as long as it doesn't impact load times for the form or cause other issues because the data load is huge). That's because if you requery the data source for the initial dropdown on each selection, you could end up with no data available if the user goes back to change an option in a prior row. Let's say your dropdowns are State and City. In row 1, the user selects WA for state. You query the city list for all cities where State = WA. User selects Seattle. In row 2, the user selects OR for state. You query the city list for all states where the State = OR. The user selects Portland. All is good so far! But now the user decides to change Seattle to Tacoma in Row 1. The State hasn't changed, so the query hasn't re-run. All the cities in the secondary list for cities are those where the State = OR. So when the user tries to change Seattle to Tacoma - all she sees is Oregon cities in the City dropdown. Make sense?
Hilary Stoupa
