[Flutter/dart] Documents that should be in the firestore cannot be extracted

Overview

I want to get only the documents that meet the conditions from the documents saved in the firestore. I made a query using where (), but I can't get the document that should be there (I confirm that it actually exists on the console).

Cause

There was a document that contains only collection. If there is such a document, it seems that it will not be queried, including the elements after that.

collection A

- document A1 ←document contains only collection

-collection B

-collection C

- document C1 ←I want to extract these documents by where()

- document C2

・・・

Solution

I could only think of putting a tentative value in a document that contained only a collection so that it could be seen.

Well, I was able to extract with where().

collection A

- document A1

　　 'dummy': 0 ←tentative value

-collection B

-collection C

- document C1 ←I want to extract these documents by where()

- document C2

・・・