Accessing to the users uid in Firebase - json

Question

I have this JSON structure:
{
"Devices" : {
"1EJ8QmEQBJfBez7PMADbftCjVff1" : {
"Device1" : {
"Category" : "Others",
"Description" : "",
"DeviceName" : "",
"ImageUrl" : ""
},
"Device2" : {
"Category" : "Chairs",
"Description" : "",
"DeviceName" : "",
"ImageUrl" : ""
},
"Device3" : {
"Category" : "Others",
"Description" : "",
"DeviceName" : "",
"ImageUrl" : ""
}
},
"97PUAcUC5UYxLpBOLnC4yQjxiEf2" : {
"Device1" : {
"Category" : "Others",
"Description" : "",
"DeviceName" : "",
"ImageUrl" : ""
},
"Device2" : {
"Category" : "Books",
"Description" : "",
"DeviceName" : "",
"ImageUrl" : ""
},
"Device3" : {
"Category" : "Chairs",
"Description" : "",
"DeviceName" : "",
"ImageUrl" : ""
}
}
},
"UserProfile" : {
"1EJ8QmEQBJfBez7PMADbftCjVff1" : {
"city" : "",
"email" : "",
"name" : "",
"phone" : ""
},
"97PUAcUC5UYxLpBOLnC4yQjxiEf2" : {
"city" : "",
"email" : "",
"name" : "",
"phone" : ""
},
}
}
I want to access to the Category node in each device?
Is that possible?
Because I want to retrieve data for all nodes that have the same category!
let ref = FIRDatabase.database().reference().child("Devices")
ref.queryOrderedByChild("Category")
I have tried to access to devices! then direct to the category!
It seems like this is not the correct way!
Don't tell me that I need to change the structure of the JSON!
Is there any way to access to the user ids'?

Answer 1

In NoSQL databases you will often have to model your data for the use-cases that you app needs. With your current data structure you can efficiently load a user's devices.
To also efficiently allow to load the devices for a category, you will have to store that information too. Here's one way to do that:
"Categories": {
"Others": {
"1EJ8QmEQBJfBez7PMADbftCjVff1_Device1": "1EJ8QmEQBJfBez7PMADbftCjVff1/Device1",
"1EJ8QmEQBJfBez7PMADbftCjVff1_Device3": "1EJ8QmEQBJfBez7PMADbftCjVff1/Device3",
"97PUAcUC5UYxLpBOLnC4yQjxiEf2_Device1": "97PUAcUC5UYxLpBOLnC4yQjxiEf2/Device1"
},
"Chairs": {
"1EJ8QmEQBJfBez7PMADbftCjVff1_Device2": "1EJ8QmEQBJfBez7PMADbftCjVff1/Device2",
"97PUAcUC5UYxLpBOLnC4yQjxiEf2_Device3": "97PUAcUC5UYxLpBOLnC4yQjxiEf2/Device3"
},
"Books": {
"97PUAcUC5UYxLpBOLnC4yQjxiEf2_Device2": "97PUAcUC5UYxLpBOLnC4yQjxiEf2/Device2"
}
}
So the above structure uses <uid>_<devicekey> as the keys and then has the path to that item under /devices as its value.
I recommend reading this great article on NoSQL data modeling.