Firebase Combining Query and Pagination - swift

Question

Query can be used to filter a large items down to a smaller number suitable for synchronizing to the client.
Pagination is a also serve the same purpose, that is to limit the items to a smaller numbers suitable to be be fetched by the client.
Consider the following database schema:
"users": {
"-KRyXWjI0X6UvffIB_Gc": {
"active": true,
"name": "John Doe",
"occupation": "Looking for firebase answer"
},
"-KRyXBWwaK112OWGw5fa": {
"active": false,
"name": "Jane Doe",
"occupation": "Still stuck on combining query and pagination"
},
"-KRyWfOg7Nj59qtoCG30": {
"active": true,
"name": "Johnnie Doe",
"occupation": "There is no greater sorrow than to recall in misery the time when we were stuck"
}
}
If I were to get all the active users, it will be like this: (Code in Swift)
let usersRef = ref.child("users");
let query = usersRef.queryOrderedByChild("active")
.queryEqualToValue(true)
After that filtering, it left me with 10,000 users. Fetching all of those users at the same time is out of question. It must be paginated.
To do the pagination, I have to do the query on the unique sorted value, which is none other than the key itself. This is how it looks now:
let usersRef = ref.child("users");
let query = usersRef.queryOrderedByChild("active")
.queryEqualToValue(true)
let usersPerPage = 10;
query.queryOrderedByKey()
.queryStartingAtValue(lastKey)
.queryLimitedToFirst(usersPerPage)
This wouldn't work because:
You can only use one order-by method at a time. Calling an order-by
method multiple times in the same query throws an error.
After I spent 2 days on thinking how am I supposed to solve this situation, I can only came up with this "anti best practice" solution.
I modified the database schema. I convert the active boolean value to the string and append it after the key to give the order importance control to the key. This is how it looks now:
"users": {
"-KRyXWjI0X6UvffIB_Gc": {
"key_active": "-KRyXWjI0X6UvffIB_Gc true"
"active": true,
"name": "John Doe",
"occupation": "Looking for firebase answer"
}
}
Now I could do both the pagination and the query using the single orderBy:
let usersPerPage = 10;
query.queryOrderedByChild("key_active")
.queryStartingAtValue("\(lastKey) true")
.queryLimitedToFirst(usersPerPage)
Somehow my brain reject the idea of having the key inside the key because it's the worst dirty solution it can be. I want to know the right solution for this particular situation, any solution would be greatly appreciated.

Answer 1

Just add this to your JSON tree:-
active_Users :{
uid1 : {
index : 1,
name : "John Doe"
},
uid2 : {
index : 2,
name : "Johnnie Doe"
}
}
After this just follow this answer :- Retrieving 5 user's at a time, modify it according to your requirements.
Note:- Total no of users/posts in that answers is being retrieved by doing children count. Given your heavy database, you might wanna store totalNoOfUser in a separate node and increment it every time a new user is added.