Trigger attribute on dropdowns fire unconditionally across a page

[lo5]

Via @FelixArokia

async def main_page(q: Q):
    q.page['main_title'] = ui.form_card(box = '4 1 5 1', items = [
                                    ui.text_xl("This is the main page"),
    ])
    store_choices = [ui.choice('Store_1', 'Store_1'), ui.choice('Store_2', 'Store_2')]
    selected_store = 'Store_1'
    q.page['store_dropdown_card'] = ui.form_card(box = '2 2 2 1', items = [
        ui.dropdown(name='arg_store_dropdown', label='Select Store', value=selected_store,
                    required=True, choices=store_choices, trigger=True),
    ])
    item_choices = [ui.choice('Item_1', 'Item_1'), ui.choice('Item_2', 'Item_2')]
    selected_item = 'Item_1'
    q.page['item_dropdown_card'] = ui.form_card(box='8 2 2 1', items = [
        ui.dropdown(name='arg_item_dropdown', label='Select Item', value=selected_item,
                    required=True, choices=item_choices, trigger=True),
    ])
    if q.args.arg_store_dropdown:
        q.page['store_trigger'] = ui.form_card(box = '1 4 10 1', items = [
        ui.text_xl("Store drop down was selected. SUCCESS STORE"),])
    if q.args.arg_item_dropdown:
        q.page['item_trigger'] = ui.form_card(box = '1 6 10 1', items = [
        ui.text_xl("Item drop down was selected. SUCCESS ITEM"),])
    await q.page.save()
listen("/trigger_working", main_page)

[lo5]

@FelixArokia I verified this. This is not a bug.

Since the value= is set on both dropdowns, q.args.arg_store_dropdown and q.args.arg_item_dropdown are initialized to those values.

When either dropdown is changed, a form submission is triggered, and hence you get back both q.args.arg_store_dropdown and q.args.arg_item_dropdown exactly as you set them. This is normal behavior.

I'm guessing that you were expecting exactly one of q.args.arg_store_dropdown or q.args.arg_item_dropdown to be set when changed, but that is not how the model works. The SDK's behavior mimics that of HTML forms: regardless of which element is changed, the values of all elements are submitted to your program.

Regardless, given that this is the behavior, and given that this cannot be changed, I'd like to know if this behavior is a show stopper for you, so that we can accommodate your case properly.

cc @mturoci

[vopani]

Q-MB has similar use-case.

This is what I do (tuned for your example):

async def main_page(q: Q):
   if not q.client.initialized:
      q.user.arg_store_dropdown = 'Store 1'
      q.user.arg_item_dropdown = 'Item 1'
      q.client.initialized = True

   if q.user.arg_store_dropdown != q.args.arg_store_dropdown:
      q.user.arg_store_dropdown = q.args.arg_store_dropdown
      q.page['store_trigger'] = ui.form_card(box = '1 4 10 1', items = [
         ui.text_xl("Store drop down was selected. SUCCESS STORE"),])
   elif q.user.arg_item_dropdown != q.args.arg_item_dropdown:
      q.user.arg_item_dropdown = q.args.arg_item_dropdown
      q.page['store_trigger'] = ui.form_card(box = '1 4 10 1', items = [
         ui.text_xl("Item drop down was selected. SUCCESS ITEM"),])

Is there a better way?

[lo5]

@vopani - thanks for the example. Assuming your example demonstrates "how to identify which dropdown was changed", is this something you commonly need, and why? Why wouldn't you blindly refer to q.args (or q.args copied over to q.user) instead of trying to identify which dropdown changed?

[vopani]

I actually refactored it to use args blindly: https://github.com/h2oai/q-marketbasket/blob/master/run.py#L634

But I can see why knowing which dropdown changed can be useful too. eg: I have a bar chart. I change a dropdown. The bar chart shows the original values (dotted) and the new values (comparing the state of the chart before the dropdown change and after). The chart would only make sense if I know what dropdown was changed and see the values before/after the change.
How would you do this without knowing which dropdown changed?

Whether it's common or not, I'm not sure but I'd say not so common. In most cases, can just use args blindly.
Maybe @FelixArokia can share his exact requirement to determine how best to solve for it.

[FelixArokia]

Not a showstopper @lo5 , I am following a very similar approach as given by @vopani here. Thanks for the clarification

[lo5]

Thanks @FelixArokia @vopani. Closing.