Styjun

First off, I'm kind of new to Firebase Database and coming from a SQL background.

I'm attempting to have a query that returns all notifications for a specified postID, regardless of which user the notification is for.

Essentially, if somebody deletes their post, I want to delete all of the "new post" notifications sent to all of their followers.

My data structure

I've tried these indexes..

 "rules": 
 ".read": "auth != null",
 ".write": "auth != null",
 "notification": 
 "$user_id": 
 ".indexOn": ["timestamp", "objectId"]
 
 
 

I can query by timestamp with the following code, and it works fine.

 dbRef.GetChild("notificaton").GetChild(userID).GetQueryOrderedByChild("timestamp");

However, I don't want to use the userID in my query for post notifications. I've searched and tried a couple of other configurations for an index, but I just get errors in the firebase db admin that there are issues with my indexes.

I believe this is because I do need to query by timestamp, so that index needs to stay. So I need two indexes for the same collection, but different configurations because of user_id not being needed for the postID index.

I'm not sure how the index needs to be configured to be able to query on objectId regardless of user_id.

I've also tried something like this..

 "rules": 
 ".read": "auth != null",
 ".write": "auth != null",
 "notification": 
 ".indexOn": ["objectId"]
 ,
 "notification": 
 "$user_id": 
 ".indexOn": ["timestamp"]
 
 
 

But I get an error Error saving rules: 'notification' occurs multiple times.

I've tried this..

 "rules": 
 ".read": "auth != null",
 ".write": "auth != null",
 "notification": 
 "$user_id": 
 ".indexOn": ["timestamp"]
 ,
 ".indexOn": ["objectId"]
 
 

And Firebase seems OK with that, as it doesn't give an error, but it also doesn't return any data, which I assume is because objectId is not on the root notification collection.

So I'm stuck.

If you want to add indexes to each user of both the timestamp and the objectId of each of their child nodes, you can do so with:

 "rules": 
 "notification": 
 "$user_id": 
 ".indexOn": ["objectId", "timestamp"]
 
 
 

This allows you to query a user for child nodes with a matching objectId, or query a user for child nodes based on the timestamp.

Firebase queries always return direct child nodes of the location you run them on. That means that the orderByChild() clause of a query must refer to a fixed path to a single property of each direct child node. In other words: you cannot query a tree.

In your case that means that you cannot search across the notifications of all users with a single query. If you want to allow that query, you'll need to store a list of notifications for all users.