How can I allow any user to access data under a "uid" in Firestore?

Question

I am building an app and I want the user to be able to tap on a URL using the URL scheme and be sent to a specific view controller on my app. That is working OK. However, I also need to get specific data onto that view controller. I need it so that User A can send an invite (URL) through Messages to User B. User B can tap on that invite (URL) to open a screen with details about the invitation from Firebase. The user can then accept the invite, or decline the invite.

I have setup my database like so:

users(collection)

"uid"(document)

parties(collection)

"partyName"(document)

respondedYes(field)

respondedNo(field)

This is the code that is in the AppDelegate for someone taps on a URL.

func application(_ application: UIApplication, handleOpen url: URL) -> Bool {
    // Open the RSVPViewController.
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let rsvpViewController = storyboard.instantiateViewController(withIdentifier: "RSVPViewController") as! RSVPViewController
    
    if let window = self.window, let rootViewController = window.rootViewController {
        var currentController = rootViewController
        while let presentedController = currentController.presentedViewController {
            currentController = presentedController
        }
        currentController.present(rsvpViewController, animated: true, completion: nil)
    }
    return true
}

I don't know how to get it so I know which invitation is being displayed after User B taps the URL so I cannot display the data. How can I get my app to work like I explained in my concept in the first paragraph? Let me know if you need more info. It is really hard to explain what I need help with.

Answer 1

In this scenario, the invite URL needs to include parameters that will tell your app which invite User B is opening. This can be achieved with simple GET params in your URL. So for instance your URL now might look like this: myapp:Invite?invite_id=2, where the invite_id param will be dealt with when User B opens the app.

Since it's not the best idea to give other user's access to data under the first user's UID, I would create a new "invitations" collection on firestore, where a new invitation document gets created when user A sends it. The UUID of the newly created invitation document would be the parameter you send in the URL above.

To create this URL, see this answer, Basically you would do the following:

let queryItems = [NSURLQueryItem(name: "invite_id", value: "123")]
let urlComps = NSURLComponents(string: "myapp:Invite")!
urlComps.queryItems = queryItems
let URL = urlComps.URL!

Now, in the application(_:,handleOpen:) (for the receiver's app) you can parse URL params by extending the URL class as explained in this answer.

Assuming you use the extension described in the linked answer(which I tested on playground before recommending here), you can rewrite your function as follows:

func application(_ application: UIApplication, handleOpen url: URL) -> Bool {

    let invite_id = url.valueOf("invite_id")

    // get data from firestore for this invite id and store it in a struct called invite_data 
    // (i'm going to assume that the variable invite_data is defined now).

    // Open the RSVPViewController.
    let storyboard = UIStoryboard(name: "Main", bundle: nil)
    let rsvpViewController = storyboard.instantiateViewController(withIdentifier: "RSVPViewController") as! RSVPViewController

    // tell the rsvpViewController about the data:
    // this assumes you have a variable in rsvpVC that takes this info to display it.
    rsvpViewController.invite_data = invite_data 

    if let window = self.window, let rootViewController = window.rootViewController {
        var currentController = rootViewController
        while let presentedController = currentController.presentedViewController {
            currentController = presentedController
        }
        currentController.present(rsvpViewController, animated: true, completion: nil)
    }
    return true
}

Note that invite_data above is a struct and can contain whatever info you need to both display relevant details in the RSVP VC plus handle things like accepting or declining invites.

An alternate approach would be to simply send all the data you want to display in the rsvpViewController and not bother with an invitation document. Might be easier if the number of fields is small. But I suspect in this scenario you will want to pass things like party_id etc, so depends on your use case.