Storing user data inside items in firebase/firestore

Question

I am building a firebase web application. Here is a simplified Firestore structure:

...
   - ...
        ITEMS
           - item1
                PHOTOS
                   - photo1
                        uid
                VIDEOS
           - item2

USERS
   - uid1
       displayName
       ... 
   - uid2
   - ...

When someone accesses a photo or video I want to display the appropriate displayName and profilePhoto for that item.

I see two possible solutions:

1. Store only user UID in items. On every load, get user data from USERS collection or Then loop in user's UIDs and connect them with item UIDs. This would be done on every call. When users update displayName or profilePhoto, there wouldn't be any problem.

2. Store user UID, displayName, and profilePhoto path on the item. When users update data I would need to run a cloud function which would then update all items with new data.

How should I approach this and is there any other approach that I should consider? I lean towards the second solution.

Answer 1

What you have are the two most common approaches. The first is commonly referred to as performing a client-side join, while the second is duplicating/denormalizing the necessary data.

Neither is pertinently better than the other, but folks who are new to NoSQL databases are typically hesitant to duplicate data so tend to gravitate to performing client-side joins.

As you gain experience in NoSQL data models, you'll learn the right questions to ask yourself. For example: how often do a display name and profile photo change in my app? If that happens infrequently, duplicating those values in each item will make my reading code a lost simpler, faster, and more scalable.

For more good reading/watching on this:

• How to write denormalized data in Firebase
• NoSQL data modeling
• Todd's excellent video series: Getting to know Cloud Firestore