Filtering a form field with two other connected fields

Hi everyone,

Say I have a form with the following connected fields:

Is there a native way to filter field C with inputs A and B (intersection)?

A= Cars…Bikes…Skates…
B= 2019…2020…2021…
C= A && B (items that fulfill both criteria)

If not, do you have a piece of code available?


Hi Tomas, I’m not sure what your use case is and am struggling to understand your request.
I’d be happy to connect so you can walk me through your scenario and see if I can offer any advice.

Hi Carl,

Sorry if it is not clear.

The question is actually quite simple: how to filter a connection field with 2 other connection fields (within a form view)?

Say you want to display a dropdown menu with vehicles that are type= cars and color= red. How do you do it?

a. Please select your type of vehicle: XYZ
b. Please select your desired color: ZXI
c. Please select an available vehicle: UIP

Knack lets us filter one connection input with another (“show b belonging to a and show c belonging to b”), but not with two others (“show c belonging to a and b”), neither with three others, etc…

That’s what I meant with “intersection”.


I’m still confused on the use case and structure.

If you have a table of Cars and a table of Colors you must already have a table that shows a record with the vehicle make, model, color, age, engine size, transmission etc

If the user is selecting a Car from one table and a Color from another table this is still only filtering the results in the same table so you can show those vehicles that match criteria.

If you want to connect it may be easier to see if I can assist :sunglasses:
I’m UK London BST, presume you are USA - EST is 5 hours behind currently.
Happy to connect on Zoom for 30 mins to see if we can get a solution.

May just be me, but the penny is not dropping regarding the structure :man_shrugging:

It seems that you want to replicate the functionality of a Search view in a Form view.

Maybe you could do that with a Text Formula field?

And then there is this related use-case, but just for filtering with one connection imput, not more as you need.

Other than that I have no idea.

Maybe first a Search view between various features.
Then in the Results table, show a button to add the vehicles that match.

Might be easier then what you are trying to do.

Hi @MichaelG - that’s kind what I was alluding to. If you have a car model and car color then a search page would give you the results. I don’t see why or how you would have a third connection combing the first two so you could select that in the record too :man_shrugging:

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Yeap @CarlHolmes . That might be a useful Feature Request actualy. Because I am also asking for something similar within a Form:

  • to first filter project collaborators among staff,
  • and from the collaborators, select one responsable.

Maybe a special Form Rules > Display Rules: show results filtered by this or various fields. Yeap, a mini Search feature inside a Form.

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