How to structure firebase DB to block USER from displaying GROUPS - ios

Question

I have 2 DB in firebase: USERS and GROUPS as structured below:
USERS
USERID
USERNAME
USEREMAIL
USERPHONE
GROUPS
GROUPID
GROUPNAME
GROUPPIC
TIMESTAMP
I logged in as user123. In the GroupsViewController, all the groups will be displayed and I have the option to block/unblock certain group(s). Once it is blocked, that particular group shouldn't be displayed in my GroupsViewController.
Now, I wanted to restructure the DB so that the blocked group will not display for that particular user (user123). I'm not sure whether to have child node BLOCKEDUSERS under GROUPS or have child node BLOCKEDGROUPS under USERS, like the below ones.
Which one is best and why? And how to show all the groups except the blocked ones
USERS
USERID
USERNAME
USEREMAIL
USERPHONE
BLOCKEDGROUPS
GROUPID
GROUPS
GROUPID
GROUPNAME
GROUPPIC
TIMESTAMP
BLOCKEDUSERS
USERID
I really appreciate your help.
Update :
I have added blockedGroups under userInfo, added some groupID to specific user.uid and created rules as you can see below. Ideally "groupID2" group should be blocked for the user "6viyeuDpC5TPbO3coElZp3LWWdH3", but the permission is denied for all the users. What I'm doing wrong?

Answer 1

You can add another DB which tracks user based permission. It should maintain all the user-specific permissions, As you are already maintaining the group id, set it as Enable/Disable the flag.
Follow instruction below
create DB user_group_permission.
Add fields user_id, group_id and status
Make status by default 1(consider it as not blocked).
When you want to block change the status to 0(consider it as not blocked).
You have to handle this in the code with an enum to make more sense to the value.
The advantage of this module is that later if you add other features other than just blocked and unblock, you will just have to increment status value to 2,3,4 and so on and update the enum.

Answer 2

You can use both structure options together if you wanted to start fanning out your data.
Using the first option of having a list of blockedGroups under the user node makes it easy to deny access to groups that the user has blocked by using Firebase security rules:
{
"rules": {
"groups": {
"$groupId": {
".read": "root.child('users').child(auth.uid)
.child('blockedGroups').child($groupId)
.exists() != true"
}
}
}
}
So your database structure would become something similar to:
users
|- userId1
|- userName: "User 1"
|- ...
|- blockedGroups
|- groupId1: true
groups
|- groupId1
|- groupName: "Group 1"
|- ...
|- groupId2
|- name: "Group 2"
|- ...
Where each user ID is a user's UID from FirebaseAuth#getUid() which will match the currently logged in user to auth.uid in the rules. And the list of blockedGroups is an index list of group IDs, like in the flatten data structures documentation example.
Unfortunately, the security rule method above won't work as a way to filter the groups list, but only as a method to deny access to specific group nodes. This is because rules are applied atomically top-down.
Instead, you'll need to retrieve the list of blockedGroups for the user, and retrieve all the groups, then do a client-side filter to ignore or discard the groups that the user doesn't want to see. Something like this in Swift:
var blockedGroups = [String]()
blockedGroupsRef.observe(.value) { snapshot in
for child in snapshot.children {
blockedGroups.append(child.key)
}
updateView()
}
func updateView() {
groupsRef.observe(.value) { snapshot in
for child in snapshot.children {
if blockedGroups.contains(child.key) == false {
// Add to view
}
}
}
}
Alternatively, depending on the requirements for your app, if you don't want to perform client-side filtering, you could flip the group management to be opt-in rather than opt-out, and use a list of subscribedGroups instead and then loop through this list to retrieve each group from the database individually by key.