Add a Document's Document ID to Its Own Firestore Document - Swift 4

Question

How do I go about adding the document ID of a document I just added to my firestore database, to said document?

I want to do this so that when a user retrieves a \"ride\

Answer 1

While there is a perfectly fine answer, FireStore has the functionality you need built in, and it doesn't require two calls to the database. In fact, it doesn't require any calls to the database.

Here's an example

    let testRef = self.db.collection("test_node")
    let someData = [
        "child_key": "child_value"
    ]

    let aDoc = testRef.document() //this creates a document with a documentID
    print(aDoc.documentID) //prints the documentID, no database interaction
    //you could add the documentID to an object etc at this point
    aDoc.setData(someData) //stores the data at that documentID

See the documentation Add a Document for more info.

In some cases, it can be useful to create a document reference with an auto-generated ID, then use the reference later. For this use case, you can call doc():

You may want to consider a slightly different approach. You can obtain the document ID in the closure following the write as well. So let's give you a cool Ride (class)

class RideClass {
    var availableSeats: Int
    var carType: String
    var dateCreated: String
    var ID: String

    init(seats: Int, car: String, createdDate: String) {
        self.availableSeats = seats
        self.carType = car
        self.dateCreated = createdDate
        self.ID = ""
    }

    func getRideDict() -> [String: Any] {
        let dict:[String: Any] = [
            "availableSeats": self.availableSeats,
            "carType": self.carType,
            "dateCreated": self.dateCreated
        ]
        return dict
    }
}

and then some code to create a ride, write it out and leverage it's auto-created documentID

    var aRide = RideClass(seats: 3, car: "Lincoln", createdDate: "20190122")

    var ref: DocumentReference? = nil
    ref = db.collection("rides").addDocument(data: aRide.getRideDict() ) { err in
        if let err = err {
            print("Error adding document: \(err)")
        } else {
            aRide.ID = ref!.documentID
            print(aRide.ID) //now you can work with the ride and know it's ID
        }
    }