CountIf and FIlter Cannot compare Detail List FK with Master ID

[PowerunAppy]

hello.

I have two Sharepoint lists - a Master List and a Detail List.  The Detail List has a Link Field that references the Master List's ID.  I had wanted to show the number of detail rows in a summary view of the Master List.

I want to use the expression

CountIf(LabVisitDetails, ThisItem.ID=LabVisitDetails.LabVisitMasterID)

to set a label in a gallery.

But powerApps studio marks the equals sign in my formula as an error.  The error message is "Invalid argument type" .  I've tried various comparisons in place of "=", but to no avail.

Is there some special syntax, or a member of either term in the equals test that I should use here?

[RandyHayes · Accepted solution]

Is LabVisitMasterID a numeric column or a Lookup?  I am assuming when you say "Link Field" you are talking about a "Lookup Column".

If it is a lookup column, then you need your syntax to look like this:

      CountIf(LabVisitDetails, LabVisitMasterID.Id=ThisItem.ID)

[PowerunAppy · Accepted solution]

I believe I may myself have found out how to do this. The Master List is the data in the Gallery, and the Detail List is to provide a Count of Visit Details for informational purposes.

The problem was as I surmised earlier due to a failure to reference the correct Member of the Link Field.

CountIf(LabVisitDetails, LabVisitDetails[@LabVisitMasterID].Id = ThisItem.ID)

In this version, I use the full reference to the Link Field In LabVisitDetails  (LabVisitDetails[@LabVisitMasterID]) and then reference the Id member of the Link Field.  This gets tested against ThisItem.ID. The CountIf runs, and emits the expected number of detail records