Finding data in Firebase from all child nodes while authenticated

I recently completed a tutorial on creating an app with Firebase sync and authentication, following the steps outlined here. However, I am now facing a challenge in querying data among all children due to their lexicographical-based keys.

Specifically, using the example provided, how can I query for all "currentCity" values from all "users"?

{
  "users" : {
    "1e2f048f-a3a0-4190-afad-81d724ed1997" : {
      "currentCity" : "Arrecifes",
      "currentCountry" : "ARG",
      "currentState" : "BSA",
      "day" : {
        "domingo" : true,
        "jueves" : true,
        "martes" : false,
        "miercoles" : true
      },
      "gender" : "Masculino",
      "name" : "Guillermo H Acosta",
      "position" : "Medio",
      "registered" : true,
      "timeSince" : "22:00",
      "timeUntil" : "23:00",
      "whereToPlay" : "Güemes"
    },
    "39c6ccf9-61ec-446e-9af3-3a87810fab71" : {
      "currentCity" : "Alvear",
      "currentCountry" : "ARG",
      "currentState" : "CRR",
      "day" : {
        "jueves" : true,
        "miercoles" : true,
        "viernes" : true
      },
      "gender" : "Masculino",
      "name" : "Guillermo Acosta",
      "registered" : true,
      "timeSince" : "21:00",
      "timeUntil" : "23:00"
    },
    "4991bdc9-dfc4-4ff5-ab81-0e28f1b3ab53" : {
      "currentCity" : "Cordoba",
      "currentCountry" : "ARG",
      "currentState" : "COR",
      "day" : {
        "miercoles" : true,
        "viernes" : true
      },
      "gender" : "Masculino",
      "name" : "Hsjja",
      "timeSince" : "02:00",
      "timeUntil" : "03:00"
    },
    "509364fd-388b-42ff-91ed-0811811a4ff3" : {
      "day" : {
        "jueves" : true,
        "lunes" : true,
        "martes" : false,
        "sabado" : true
      },
      "name" : "Guillermo Acosta",
      "position" : "Delantero",
      "timeSince" : "13:00",
      "timeUntil" : "14:00",
      "whereToPlay" : "Güemes"
    }
  }
}
angularjsionic-frameworkfirebaseangularfirefirebase-realtime-database

Answer №1

When using the Firebase Database, you can either retrieve a complete node or not get it at all. It is not possible to fetch specific parts of different nodes in a single query.

For example, if you only require the cities associated with each user, it would be best to store this information in a separate node:

{
  "userCurrentCities" : {
    "1e2f048f-a3a0-4190-afad-81d724ed1997" : "Arrecifes",
    "39c6ccf9-61ec-446e-9af3-3a87810fab71" : "Alvear",
    "4991bdc9-dfc4-4ff5-ab81-0e28f1b3ab53" : "Cordoba",
  }
}

Answer №2

In this code snippet, the program goes through each node and extracts the value of the currentCity key. If the currentCity value is NULLABLE, it is advisable to store it in a separate node.

let ref = // specify path to users here
ref.observeEventType(FIRDataEventType.Value, withBlock: { (snapshot) in
    // Store all user data in a dictionary
    let postDict = snapshot.value as! [String : AnyObject]
    for user in postDict {
        // Convert child objects of the user into dictionaries
        let data = activity.1 as! [String : AnyObject]

        // Retrieve the specific child named currentCity
        let currentCity = children["currentCity"] as! String

        // Process the extracted data
        print(currentCity)
    }
})

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