query_city.kt

data class City(
    val name: String? = null,
    val state: String? = null,
    val country: String? = null,
    val isCapital: Boolean? = null,
    val population: Long? = null,
    val regions: List<String>? = null
)

db.collection("cities")
    .whereGreaterThan("population", 1000000)
    .get()
    .addOnSuccessListener { snapshot ->
        for (doc in snapshot) {
            val city = doc.toObject(City::class.java)
            displayCity(city)
        }
    }