How to get random documents from Cloud Firestore in Dart (for Flutter)? [closed]

Answer 1

According to Dan's answer, here's my current implementation.

static const AUTO_ID_ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
static const AUTO_ID_LENGTH = 20;
  String _getAutoId() {
    final buffer = StringBuffer();
    final random = Random.secure();

    final maxRandom = AUTO_ID_ALPHABET.length;

    for (int i = 0; i < AUTO_ID_LENGTH; i++) {
      buffer.write(AUTO_ID_ALPHABET[random.nextInt(maxRandom)]);
    }
    return buffer.toString();
  }

Code to query:

final autoId = _getAutoId();

final query = ref
    .where("qId", isGreaterThanOrEqualTo: autoId)
    .orderBy("qId")
    .limit(count);
QuerySnapshot response = await query.getDocuments();
if (response.documents == null || response.documents.length == 0) {
  final anotherQuery = ref
      .where('qId', isLessThan: autoId)
      .orderBy('qId')
      .limit(count);
  response = await anotherQuery.getDocuments();
}

Some explainations:

1. qId is a field of my document. It's same as the documentId.
2. This implementation is based on Bi-directional, according to Dan's answer. We still have unfairly result but I'm ok with that. If someone have better algorithm, please share.
3. _getAutoId() is re-written based on Java code of firebase library.

If you have any questions, please ask. I will try to help as much as I could.

Have a nice day!