firestore.rules

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /participant_responses/{studyID}/participants/{participantID} {
      allow create, read: 
      if 
        // Allows any combination of studyID and participantID to be created in Firebase
        true
        // participantID must be in the registered_participants array in the registered_studies/{studyID} document
        // participantID in get(/databases/$(database)/documents/registered_studies/$(studyID)).data.registered_participants;

      // experimentID must be in the data subcollection
      match /data/{experimentID} {
        allow create, read: if true

        // trialID must be in the trials subcollection
        match /trials/{trialID} {
          allow create, read: if true
        }
      }
    }
    }
}