Retreive data from Firebase

Question

I have been trying (without success) to retrieve a list of users in a group from a Firebase database; and I was wondering if its possible based on my data structure (below), or is the problem my swift code (also below)

This is my Firebase structure:

Users
---- <UserID>
---------- Username
---------- Email
---------- etc...
Groups
---- <GroupID>
---------- GroupName
---------- CreationDate
---------- GroupAdmin
---------- etc...
UsersInGroups
------- UserID
---------- GroupID : true   <---- User is in Group

With the above data structure is it possible for me to retrieve the list of all users in the a particular group?

Currently my swift code is as follows:

ref = Database.database()reference(withPath: "UsersInGroups")
handle = ref.queryOrdered(byChild: <userID>).queryEqual(toValue: true).observe(.value, ....

As you can imagine, it is not pulling the userID where the groupID = true!?

Lastly, I was wondering if this is possible: I would like to get a list of all the GroupEntries a User has done.

the Firebase structure is as follows:

GroupEntry
-------- <GroupID>
--------------- <entryID> : <userID>

the is a dynamic and unique string (ex 3:8) and the userID is the user that created the entry.

The swift code is below:

ref = Database.database()reference(withPath: "GroupEntry")
handle = ref.child(<groupID>).queryEqual(toValue: <userID>).observe(.value, ...

Can anyone offer any assistance!?

This is a categorization problem. The best solution is to add an additional top-level list of `GroupUsers` (the inverse of your `UsersInGroups`. See http://stackoverflow.com/questions/40656589/firebase-query-if-child-of-child-contains-a-value — Frank van Puffelen, Nov 24 '17 at 18:55
@FrankvanPuffelen thats what I was figuring... I just didnt want to face the facts.... :( How about the second portion, do I need to do the same thing!? I hope not!? — Learn2Code, Nov 24 '17 at 19:14

Callam · Answer 1 · 2017-11-24T19:10:25.360

You can represent the relationships between the groups and users using the following locations:

group-users/$groupId/$uid
user-groups/$uid/$groupId

Storing both inversions of the relationship will give you more querying abilities. To retrieve the users in a group, you observe the children at group-users/$groupId – on the other hand, you can get the groups a user is in by observing the children at user-groups/$userId.

Group entries can be represented with two more locations:

group-entries/$groupId/$entryId
user-entries/$userId/$entryId

You could get all the entries a user has made by observing user-entries/$userId; you can query further by ordering by the child that contains the entry's $groupId.

The challenge with all of these locations is maintaining them – ensuring that data is kept consistent throughout. This can be in a somewhat manual way using one of the Firebase client SDKs, however you could consider using Cloud Functions to create triggers that update the relevant locations in the database.

Retreive data from Firebase

1 Answers1