CODEWITHSUNDEEP
firebasegoogle-cloud-firestorenosql
Alex Stroescu
Alex Stroescu

Reputation: 1158

Firestore model for fetching a list of friends of an user

I have been using Firestore for a very long time. I am building an app now where scalability and keeping low costs is important. (I am using flutter)

My app has users, which have user profiles, also they can add friends and talk to them (like instagram or facebook). I have a problem building this friends system.

My model for this friends system currently looks like this:

  1. Users collection. Each document id = user id from auth, those docs contain data like name, username, profile picture, etc.
  2. Friends collection. Each document id = user id from auth. For each user, those docs contain a field called: friends, which is an array with each of his friends user ids. The model looks like:
Friends collection:
    - uid:
        - friends_list: [friend_uid1, friend_uid2, ...]

This is how my "backend" looks. Now I want to show my user a list of his friends. How do I do that?

I want a list that looks like instagram, with a nice UI showing each of my user friend profile pic, name, last message, etc.

I can not find a straight forward way to do this with Firestore and queries.

Let's say I do it like this:

  1. Get all my friends user ids in an array.
  2. Get all their user documents using .get() for each document.

This is not doable in firestore cause it would eliminate all the querying power I have (such being able to query only for users with name "x"), I would have to fetch all users and do the query on my front-end (or in a cloud function, same thing, not scalable).

If I do this like:

  1. Get all document using a query for all users in the Friends collection, where friends_list contains my user id.
  2. Save from those documents only the documentID and fetch all the friends user data manually.

This comes with another problem. In Firestore there is no way of fetching a document without fetching all of its fields, so the first query which I use to get the ids only of my friends would actually give me their id + their friend list instead (cause when I query, it also gets the document id + the data), which is not good.

If I do it like:

  1. When you add a friend, instead of just saving its uid, save its uid + data.
  2. Now I can easily show my user his friends list nicely and do some querying on front-end.

The problem here is that now if one of my friends updates his profile photo, I need to update it in every document of all of his friends, which is very write expensive for just a little profile update.

There is also the problem of watching for more data, maybe I have another collection with Chats, and I want to show the last message of my chat with a friend, now I have to fetch the chat rooms too, which is more hard to query data that comes with all the problems that I mentioned before.

In conclusion: I don't see a good scalable way to do this kind of system within Firestore. It seems a simple system which any basic app should have, but I do not see how I can do it in a way that does not make lots of reads or read more data (or sensitive data) than it should.

What kind of model would you do for a friends system like this?

Upvotes: 2

Views: 1421

Answers (1)

jalcala
jalcala

Reputation: 63

You're decribing a quintessential drawback of NoSQL Databases. A similar example is actually given in the Get to Know Cloud Firestore series.

Like others have commented, the answer really depends on your application. And this is the assessment you'll have to do. Like which of the options is cheaper depending on the use case of the app.

For example, if you go with your third option and store the friend's user data that you'll need to populate the list. This means you'll have to implement measures to keep the integrity of the copied data whenever the user updates their information.

You can then look at the usage of your app and determine how often users change their information vs how often you would need to retrieve full users if you don't copy the data to find the cheapest method for your application.

Upvotes: 2

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