how to get a username in firestore from another collection with angularfire

Question

how to get a username in firestore from another collection with angularfire

I have 2 collections

-users
--username
--uid

and

-post
--title
--user_id

How to get the username when displaying all posts?

I could only return the user_id

Answer 1

You didn't share your existing code for displaying all posts, so it is difficult to give your the exact code to add...

But, basically, you have two options:

Lookup the username in the users collection

Before displaying a post , you do an extra query to the database to get the value of the username , like afs.collection('users', ref => ref.where('uid', '==', 'user_id)) (See https://github.com/angular/angularfire/blob/master/docs/firestore/querying-collections.md )

This implies an extra read for each post you display

Save the username together with the userid when you save the post document

This is a classical approach in the NoSQL world: you denormalize your data in such a way your query is easy to build and execute.

More concretely it means that your posts collection would be like:

-post
--title
--user_id
--username

However, this is only possible if you have, in your front-end, the value of username when you write the post document. One classical way is to get it from the currentuser object, via currentuser.displayname .

One side effect of this approach is that you need to keep the values in sync (ie the one in the user document and the ones in the post document s ). However, in your specific case, we can probably make the assumption that the username is not going to change very frequently...

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You should not be afraid to duplicate data and denormalize your data model. Here is a "famous" post about NoSQL data-modelling approaches: https://highlyscalable.wordpress.com/2012/03/01/nosql-data-modeling-techniques/