Firebase data structure - Keeping duplicated data up-to-date - firebase

Question

I created a flatted data structure. When pushing duplicated data whats the accepted pattern for keeping that data up-to-date. Here the data for the groups info is duplicated into the users-groups and the groups tree.
{
"users": ..
"users-groups": ..
"groups": ..
}
When creating a group for a user two updates takes place:
First: push to /groups/group_key
{
"name": "Test Group",
"image: "/testimage.jpg"
}
Second: push to /users-groups/user_uid/group_key
{
"orderNum: 0,
"info": {
"name": "Test Group",
"image: "/testimage.jpg"
}
}
Should keeping this data in the user-groups up-to-date be a job for the client or should a server handle this?
The data in the groups tree will always be the newest and the changes should propagate down to all the users that are members of that group.
Is there any tutorials or reference material for this problem?
note: i'm using this structure because a user can be a member of multiple groups and I don't think it would be a good idea to make possibly several ref.once's to get the data from the /groups/ directly.

Answer 1

You can use multi path update. Just observe reference with function and update all other informations
db.ref("").update({
'/users/dedd': info,
'/users/cdcd': info2
})

Answer 2

You should not have data saved duplicated. Instead you should save reference to group.
Your data should look like this.
{
"users": {
"userkey1": {
"data": {
"name": "",
"firstname": ""
},
"groups": {
"groupkey1": true // true or orderNum value
}
}
},
"groups": {
"groupkey1": {
"data": {
"name": "Test Group",
"image": "/testimage.jpg",
"other": "data"
},
"users": {
"userkey1": true
}
}
}
}
You can easily check if user is in group by checking if value at any of these positions is true.
users/userkey1/groups/groupkey1 or groups/groupkey1/users/userkey1.
When you create new group you save in under groups/newgroupkey position and you updated groups under users node by only setting newgroupkey to true.
So you do not duplicate your data.
For more information about structuring your data check the following link.
https://firebase.google.com/docs/database/android/structure-data