How to isolate data by groups of users in firebase - firebase

Question

I’m fairly new to Firebase and its json database. So right now I’m designing the tree hierarchy but when reading the documentation it says that “when you fetch data at a location in your database, you also retrieve all of its child nodes”.
I understand that this means that if you have this
a1
—b1
——c1
——c2
———d1
———d2
———d3
———d4
—b2
——c1
——c2
———etc…
and you want to fetch “c1”, you will download not just “c1” but “c2” and all “d”s. And it makes sense BUT in the example in the documentation it says that to list all “c1”s requires to download the whole tree from “a1”.
Am I correct? And if so, how can I model a tree where I need to isolate data by groups of users and all their internal shared info?

Answer 1

You can address each node in your tree by creating a reference to it. But if you retrieve the value for a node, you will also get each node under it.
So if you attach a listener to /a1/b1:
var root = firebase.database().ref();
root.child('a1/b1').on('value', ...
You will get c1, c2, d1, d2, d3 and d4.
But if you address the c1 directly, you will get only that node:
root.child('a1/b1/c1').on('value', ...

Answer 2

I have some nice examples for you.
You can't access a user's "name" without also downloading all of it's posts in this case:
{
"users": {
"user1": {
"name": "John",
"posts": {
"post1": {...},
"post2": {...}
}
},
"user2": {
"name": "Nate",
"posts": {
"post1": {...},
"post2": {...}
}
},
"user3": {
"name": "Buck",
"posts": {
"post1": {...},
"post2": {...}
}
}
}
}
Denormalize your database for better data querying and fetching:
{
"users": {
"user1": {
"name": "John",
"posts": {
"post2": true,
"post5": true
}
},
"user2": {
"name": "Nate",
"posts": {
"post1": true,
"post6": true
}
},
"user3": {
"name": "Buck",
"posts": {
"post3": true,
"post4": true
}
}
},
"posts":{
"post1":{
...,
"user":"user2"
},
"post2":{
...,
"user":"user1"
},
"post3":{
...,
"user":"user3"
},
"post4":{
...,
"user":"user3"
},
"post5":{
...,
"user":"user1"
},
"post6":{
...,
"user":"user2"
},
}
}