Search for particular value under all nodes in a directory - swift

Question

I am struggling to figure out how to delete/look for a certain key/id under any given node in a particular directory.
Here is how my database looks:
The userID and postID is generated through the use of .childByAutoId(). So as you can infer, searching by a particular string .e.g. a username, is not possible. However, I do have the postID passed through the parameters, when calling the function. I have tried several methods, but no luck. In essence this is what I wish to do (pseudo code):
Go to the "feed" directory
The postID is passed already, so look through every node under feed
If the postID exists under a particular node, remove the node, if not, move onto the next node
Continue until the node does not exist in this particular directory
I do have a reference to my feed directory - API.Feed.REF_FEED. I have tried to use .parent , .queryOrdered, .queryEqualTo etc.

Answer 1

This will work:
let query = feedRef.queryOrdered(byChild: "-L....VJ").equalTo(true)
query.observe(.childAdded, with: { (snapshot) -> Void in
snapshot.ref.removeValue()
})
The problem with this approach though it that it requires that you have an index on -L....VJ, and thus on every post ID that you might want to delete. This rapidly becomes unmanageable.
For this reason consider adding an inverted lookup map to your database: one that maps each post ID to the users that have that post in their feed:
userposts
$postid
userid1: true
userid2: true
Now you can quickly find all the users that have a specific post, and then delete the post from those users' feed.