CODEWITHSUNDEEP
iosswiftfirebasefirebase-realtime-database
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Reputation: 755

Retrieve list of a particular value for a key from Firebase

I have below firebase structure:

2014 {
 0 {
  CityState: "New York, NY",
  PinCode: "12345"
 },
 1 {
  CityState: "Los Angeles, CA",
  PinCode: "67890"
 }
}

I have to get list of all the CityState field from the firebase database. But I always get full data and then have to filter the data like below:

ref?.child("2014").observeSingleEvent(of: .value, with: { snapshot in
            if let item = snapshot.value as? [Dictionary<String, Any>] {
                for items in item {
                    print(items["CityState"])
                }
            } else {
                print (snapshot.value)
            }
        })

It takes too long time because of huge data to be retrieved. Is there a firebase query where I can get list of values of "CityState" key?

I am using swift 3.2 and Xcode 9.2

Upvotes: 0

Views: 716

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 599041

Firebase always returns full nodes from the database. There is no API to get a subset of each node.

When using the Firebase Database (and most other NoSQL databases) it is recommended to model the data for the use-cases of your app. So if you need to show a list of city states in your app, you should probably store a list of city states in your database:

CityStates: {
 0: "New York, NY",
 1: "Los Angeles, CA"
}

If you want to show the city states for only a specific year, it might be worth also storing them by year (as your original JSON does):

CityStates: {
  2014 {
   0: "New York, NY",
   1: "Los Angeles, CA"
 }
}

With these structures, reading the data from your app becomes trivial and you're reading no more data than what you need to display in your app.

Note: The above structure stores the city states in an array-like structure. If the order is not important, consider storing them in a set-like structure:

CityStates: {
  2014 {
   "Los Angeles, CA": true,
   "New York, NY": true
 }
}

The advantage of this structure is that there can't be any duplicates, since keys are by definition guaranteed to be unique within a parent node.

Upvotes: 2

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