How can I check if a document contains a value inside a Firestore array?

Question

I'm using Flutter and Firestore, where is this database I'm trying to be able to see if a value exists inside an array, but I only found solutions that didn't work for me, sometimes they were in another language, but I want to be able to see if a value exists inside an array in a document.

for example, I want to check if the user id userID1 is inside the array miembros marked in red in the following image

the idea is that I can do an if to add the value userID1 if it doesn't exist in the miembros array. actually thank you very much for any help

Answer 1

If you just need to check if an array contains a specific value, then you can use arrayContains as shown below:

FirebaseFirestore.instance
  .collection('grupos')
  .where('miembros', arrayContains: 'ValueToCheck')
  .get()
  .then(...);

However, you can use arrayUnion() instead that will add the value if it's missing else it won't:

Firestore.instance
  .collection('grupos')
  .document('grupoId4')
  .updateData({ 'array':FieldValue.arrayUnion('ValueToAddInArray') });

Answer 2

I found the solution, it turns out that the following can be done when one knows the document ID.

firestoreRef.where(FieldPath.documentId, isEqualTo: docID).snapshots();

by adding in where the FieldPath.documentId, isEqualTo: docID we can search based on the document id, after this we can do a forEach or whatever is estimated in the case.