How to get a group of objects from Firebase? - ios

Question

In my React-Native app, I have an array of specific users whose values I want to pull from Firebase. What is the most efficient way to go about this? Currently I am looping through the array and making a new request for each (relevant code below):
const usersRef = new Firebase(`${ config.FIREBASE_ROOT }/users`)
for (var key in usersArray) {
var userRef = usersRef.child(key);
//do stuff here
}
However, I feel this isn't very efficient and it makes several requests to the database. Is there a way I can pass in the array and get those items from Firebase, all in one call? Thanks.
Firebase data structure:
{
"items" : [ {
"description" : "fuzzy socks",
"type" : "toy"
}, {
"description" : "bouncy ball",
"type" : "toy"
}, {
"description" : "scrabble",
"type" : "game"
}, {
"description" : "construction paper",
"type" : "crafts"
} ],
"users" : [ {
"itemList" : [ 1, 2, 3, 4 ],
"description" : "brown",
}, {
"itemList" : [ 5, 6, 7 ],
"description" : "green",
}, {
"itemList" : [ 8, 9, 10 ],
"description" : "blue",
}, {
"itemList" : [ 11, 12, 13 ],
"description" : "yellow",
} ]
}
Simplified use case: In one use case, I only want to get information about 2 of the users (out of all the users I have stored in Firebase--assume it's many more than just the 4 in the structure above). So, I have the array importantUsers:
var importantUsers = [0, 3]
Then, I want to send a request to Firebase that only queries the database for the values associated with these userID values (so somehow pass in the array to Firebase for a result). Return values would be something like this:
0: itemList: [1,2,3,4], description: brown
3: itemList: [11,12,13], description: yellow
My motivation for querying the database for multiple users at once (rather than creating a separate ref for user 0 and user 3) is to not have multiple calls made to Firebase. Is there any way to go about this?

Answer 1

So what you are after is an sql 'in' type query. Select in [0,2]. To select a number of users from a list.
The additional challenge in your question is that users you are interested in are random so you can't use .startAt and .endAt, and there is no other relation between the users.
Firebase does not have direct support for 'in', 'and' or 'or' kinds of query but there are a number of ways to make it happen.
How about this: flag the users you want and then with a single query, read them in.
First, you'll start with a typical Firebase /users node with the addition of a 'selected' child node (this can be omitted initially but I am showing it here as a placeholder)
users
uid_0
name: "Bud"
selected: false
uid_1
name: "Henry"
selected: false
uid_2
name: "Billy"
selected: false
Then, we need some random uid's, say uid_0 and uid_2 and store those in an array. Keep in mind that we would be using the Firebase generated uid but we'll use uid_0, uid_1 etc for simplicity.
With just two users, you could just observeSingleEventOfType on each of the two nodes, no big deal.
However, if we needed 100 random users or 1000, doing 1000 separate queries or observeSingleEvent's should be avoided. But, setValue is blisteringly fast (no returned data) so....
Get our users ref
let usersRef = myRootRef.ChildbyAppendingPath("users")
We know the path to each of the 100 users we want by iterating over the array to build those refs and set selected to true
for uid in uidArray {
let thisUserRef = usersRef.childByAppendingPath(uid)
let selectedRef = thisUserRef.childByAppendingPath("selected")
selectedRef.setValue(true)
}
Then, you can query for all users in the usersRef where the selected child = true.
Once you have them, to clean up, iterate over the returned users and set the selected to false or nil
The cool thing about this is that setValue can blast through 100 or 1000 users very quickly with no overhead, setting their selected child to true. Then a single query can return the values you want.
Seems almost reverse in logic to write out to then read back in but I am pretty sure it's considerably better than iterating over an array and generating 1000 queries or observers.
(Firebase folks can check me on that one)
One other thought is that if a user is say, clicking on other users in a list, you could set selected = true as they are clicking and then query for those when the user is done.

Answer 2

You could use bindAsArray or bindAsObject from ReactFire
var ref = new Firebase("https://<YOUR-FIREBASE-APP>.firebaseio.com/items");
this.bindAsArray(ref, "items");
Then you could loop over that array/object as needed without extra queries