Firestore data model for events planning app

user3214545 0
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I am new to Firestore and building an event planning app but I am unsure what the best way to structure the data is taking into account the speed of queries and Firestore costs based on reads etc. In both options I can think of, I have a users collection and an events collection

Option 1: In the users collection, each user has an array of eventIds for events they are hosting and also events they are attending. Then I query the events collection for those eventIds of that user so I can list the appropriate events to the user

Option 2: For each event in the events collection, there is a hostId and an array of attendeeIds. So I would query the events collection for events where the hostID === user.id and where attendeeIds.includes(user.id)

I am trying to figure out which is best from a performance and a costs perspective taking into account there could be thousands of events to iterate through. Is it better to search events collections by an eventId as it will stop iterating when all events are found or is that slow since it will be searching for one eventId at a time? Maybe there is a better way to do this than I haven't mentioned above. Would really appreciate the feedback.

database-design google-cloud-platform google-cloud-firestore firebase
2 Answers

I would recommend going with option 2 because it might save you some reads:

  1. You won't have to query the user's document in the first place and then run another query like where(documentId(), "in", [...userEvents]) or fetch each of them individually if you have many.
  2. When trying to write security rules, you can directly check if an event belongs to the user trying to update the event by resource.data.hostId == request.auth.uid.

When using the first option, you'll have to query the user's document in security rules to check if this eventID is present in that events array (that may cost you another read). Checkout the documentation for more information on billing.

Dharmaraj0

In addition to @Dharmaraj answer, please note that none of the solutions is better than the other in terms of performance. In Firestore, the query performance depends on the number of documents you request (read) and not on the number of documents you are searching. It doesn't really matter if you search 10 documents in a collection of 100 documents or in a collection that contains 100 million documents, the response time will always be the same.

From a billing perspective, yes, the first solution will imply an additional document to read, since you first need to actually read the user document. However, reading the array and getting all the corresponding events will also be very fast.

Please bear in mind, that in the NoSQL world, we are always structuring a database according to the queries that we intend to perform. So if a query returns the documents that you're interested in, and produces the fewest reads, then that's the solution you should go ahead with. Also remember, that you'll always have to pay a number of reads that is equal to the number of documents the query returns.

Regarding security, both solutions can be secured relatively easily. Now it's up to you to decide which one works better for your use case.

Alex Mamo0
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