Using “array-contains” Query for Cloud Firestore Social Media Structure

Question

I have a data structure that consists of a collection, called \"Polls.\" \"Polls\" has several documents that have randomly generated ID\'s. Within those documents, there is

Answer 1

I did a real-time polls system, here is my implementation:

I made a polls collection where each document has a unique identifier, a title and an array of answers.

Also, each document has a subcollection called answers where each answer has a title and the total of distributed counters in their own shards subcollection.

Example :

polls/
  [pollID]
    - title: 'Some poll'
    - answers: ['yolo' ...]
    answers/
      [answerID]
        - title: 'yolo'
        - num_shards: 2
        shards/
          [1]
            - count: 2
          [2]
            - count: 16

I made another collection called votes where each document is a composite key of userId_pollId so I can keep tracking if the user has already voted a poll. Each document holds the pollId, the userId, the answerId...

When a document is created, I trigger a Cloud Function that grab the pollId and the answerId and I increment a random shard counter in this answerId's shards subcollection, using a transaction.

Finaly, on the client-side, I reduce the count value of each shards of each answers of a poll to calculate the total.

For the following stuff, you can do the same thing using a middle-man collection called "following", where each document is a composite key of userAid_userBid so you can track easily which user is following another user without breaking firestore's limits.