Saving Data on Android

Performing queries
Sometimes, you don't want to read just the documents of certain collections. 
Sometimes you need to filter out, match by values, or simply skip a certain amount 
of documents. To do this, you use database 
queries
. Since you don't have any nested 
documents in the 
posts
 collection, let's add something to make it a bit more 
complex.
Adding comments
Saving Data on Android
Chapter 18: Reading Data from Cloud Firestore
raywenderlich.com
264

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There's one more feature that you have in the Realtime Database version of the 
WhatsUp
 app that's you didn't add, and that is the ability to add a comment to the 
post. You'll add that now and you'll use that feature to see how the queries are 
performed.
Open