How to create the following data structure in a NoSQL environment

Question

Intro
I have a FireStore database similar to a social media db, with 3 collections Users, Events, and EventUpdates. My goal is to create a feed with eventUpdates created by me and my friends. So i have to expand my database with friendship connections. But i struggle with 3 problems, and hopefully somebody here can push me in the right direction to solve these.

Problem/Question 1:
I added username and user image to the EventUpdate model so it's easier to query. I've heard denormalise is the way to go in a NoSQL database. But if a user updates his user image, i've to update all eventUpdates created by that user. Sounds like something you don't wanne do. But is there a better way to do this?

Problem/Question 2:
How can i create a data structure that is optimised for performing the following query: get eventUpdates from me and my friends ordered by date.

Problem/Question 3:
How to store likes? I can keep a counter in a eventUpdate. But this becomes a problem when i denormalise eventUpdates (see current solution underneath EDIT)..

Data structure example .

{
  "users": {
    "1": { "name": "Jack", "imageUrl": "http://lorempixel.nl" }
  },
  "events": {
    "A": { 
      "name": "BeerFestival", 
      "date": "2018/09/05",
      "creatorId": "1"
    }
  },
  "eventUpdates": {
    "1": {
      "timestamp": "13243543",
      "creatorId: "1",
      "creatorName": "Jack",
      "creatorImageUrl": "http://lorempixel.nl",
      "eventId": "A",
      "message": "Lorem ipsum"
    }
  }
}

EDIT

OK, after some trial and error i ended up with the following structure. This structure seems work, but my problem with this solution is that i need to make a lot of write calls to update a single eventUpdate because of all the copies in each feed (1000 followers means 1000 copies). And it looks like i need to do that a lot.

I would like for example to add a like button to each event update. This trigger an update on all EventUpdate copies. For me it looks like firebase is not suited for my project and i'm thinking of replacing it with a SQL DB, or can anyone here change my mind with a better solution?

{
  "users": {
    "user1": { "name": "Jack", 
      "imageUrl": "http://lorempixel.nl",
      "followers": ["user1"]
    }
  },
  "feeds": {
    "user1": {
      "eventUpdates": {
        "1": {
          "timestamp": "13243543",
          "creatorId: "1",
          "eventId": "A",
          "message": "Lorem ipsum"
        }
      },
      "following": {
        "user1": { 
          "name": "Jack", 
          "imageUrl": "http://lorempixel.nl",
          "followers": ["user1"]
        }
      }
  },
  "events": {
    "A": { 
      "name": "BeerFestival", 
      "date": "2018/09/05",
      "creatorId": "1"
    }
  }
}

In Firestore you can use a Reference as a field value. When you are denormalizing, use references to point to things that can change. If it can't or shouldn't change, then use a value. Next, you'll want to do async loading of your messages. First, retrieve the list of messages, then resolve the references. There are many options depending on the technology you are using, but essentially just run a second query. Firestore will cache results on the device so subsequent queries to the same document will just return cached. — James Poag, Sep 21 '18 at 14:56

Alex Mamo · Accepted Answer · 2018-12-05T11:46:23.257

I added username and user image to the EventUpdate model so it's easier to query. I've heard denormalise is the way to go in a NoSQL database.

That's right, denormalization and is a common practice when it comes to Firebase. If you are new to NoQSL databases, I recommend you see this video, Denormalization is normal with the Firebase Database for a better understanding. It is for Firebase realtime database but same rules apply to Cloud Firestore.

But if a user updates his user image, i've to update all eventUpdates created by that user. Sounds like something you don't wanne do. But is there a better way to do this?

Yes, that's also correct. You need to update all the places where that image exists. Because you have chosen google-cloud-firestore as a tag, I recommend you see my answer from this post because in case of many write operations, Firestore might be a little costly. Please also see Firestore pricing plans.

Regarding Firestore, instead of holding an entire object you can only hold a reference to a picture. In this case, there is nothing that you need to update. It's always a trade between these two techniques and unfortunately there is no way between. You either hold objects or only references to objects. For that, please see my answer from this post.

How can i create a data structure that is optimised for performing the following query: get eventUpdates from me and my friends ordered by date.

As I see, your schema is more a Firebase realtime database schema more than a Cloud Firestore. And to answer to your question, yes you can create. So talking about Firestore, you can create a collection named eventUpdates that can hold eventUpdate objects and to query it according to a timestamp, a query like this is needed:

FirebaseFirestore rootRef = FirebaseFirestore.getInstance();
CollectionReference eventUpdatesRef = rootRef.collection("eventUpdates");
Query query = eventUpdatesRef.orderBy("timestamp", Query.Direction.ASCENDING);

But please note that the timestamp field should be of type Date and not long. Please also take a look at my answer from this post, to see how you can add a date property in a Cloud Firestore database.

How to store likes? I can keep a counter in a eventUpdate. But this becomes a problem when i denormalise eventUpdates (see current solution underneath EDIT)

You can simply add likes but I recommend you see the last part of my answer from this post. So you might consider adding that count in a Firebase realtime database rather than in Cloud Firestore. Both databases work very well together.

This structure seems work, but my problem with this solution is that i need to make a lot of write calls to update a single eventUpdate because of all the copies in each feed (1000 followers means 1000 copies). And it looks like i need to do that a lot.

You might also take a look at my answer from this post.

For me it looks like firebase is not suited for my project and i'm thinking of replacing it with a SQL DB, or can anyone here change my mind with a better solution?

I don't think this way. There are many apps out there that have the exact mechanism as yours and are working very well.

Thanks, a lot of helpful information. I've got something in mind how i would to refactor my structure, but still need to implement it and see how it performs. — Luciano, Dec 14 '18 at 19:37
You're welcome Luciano! And if you'll have any other concerns, just post another question, so me or other Firebase developers can help you. Cheers! — Alex Mamo, Dec 14 '18 at 19:43

score 0 · Answer 2 · answered Dec 03 '18 at 10:30

If you want your feed items to be in sync with the real users data (new profile image when the user changes it for example) you can simply store the user ID in the eventUpdate document. This way you don't have to keep them in sync manually, and every time you have to display the item in the feed you could simply fetch user data, and easily query many eventUpdates on userId and created_at fields ( assuming you have them ).

To implement likes in your feed the solution depends on a bunch of things like traffic volume. The simplest way is to update a likes field with a transaction, but Firestore has a maximum updates frequency on a single document of 1 second. Plus, a transaction can easily fail if more than 5 transactions are trying to update the same document.

To implement a more solid likes system take a look at this page from the official Firebase docs.

Jesse Lima · Answer 3 · 2018-12-06T12:17:54.020

Firestore has a different approach to the NoSQL world. Once you know the data you will use (as You already do) there are some very important points about what architecture the data will have. And It depends a lot about how the data grows, what kind of queries you will need and how often you will use them. Some cases You can create a root collection that aggregates data and queries might be easier.

There is a great video from Firebase Channel that might help. Check it out! How to Structure Your Data | Get to Know Cloud Firestore #5 https://www.youtube.com/watch?v=haMOUb3KVSo

[UPDATED] December 26th

Others videos that might help to model and query your data is these videos:

How to Connect Firebase Users to their Data - 3 Methods https://www.youtube.com/watch?v=jm66TSlVtcc

How to NOT get a 30K Firebase Bill https://www.youtube.com/watch?v=Lb-Pnytoi-8

Model Relational Data in Firestore NoSQL https://www.youtube.com/watch?v=jm66TSlVtcc

How to create the following data structure in a NoSQL environment

3 Answers3