Concatenating a SoundCloud Playlist Update JSON

Question

I am currently working on an implementation of SoundCloud for a 3rd party iOS app, and as there is no SDK anymore I am doing all my calls via Alamofire.

This is what SC expects you to send in your body params:

{ "playlist":
    {"tracks":[
        {"id":"__"}, 
        {"id":"__"}, 
        {"id":"__"}]
    }
}

I hand over the current playlist where the song should be added in the playlist object to extract all the ids from tracks that are part of it atm - as SC expects you so send all the old track ids + your new one in a .PUT call

This is what the ID dance looks at the moment:

var allTracks = [Int]() //SC track id comes in as an Int

allTracks.append(trackId) //trackId is the new track

for track in playlist.tracks {
    var I = track.id
    allTracks.append(I)
}

var myparams = Dictionary<String,AnyObject>() //my Alamofire body-params

var myTracks = [Dictionary<String,AnyObject>]()

for id in allTracks {
    var D = ["id":id]
    myTracks.append(D)
}

myparams["playlist"] = ["tracks":myTracks]

As I am still fairly new to Swift/iOS Development I was looking for a more elegant way than to just throw stuff around 3x and end up basically appending it the way it came in.

Answer 1

You can make this easier with mapping.

So, let's clarify what we have.

• playlist.tracks - An array of "tracks" which have an id property (which is what we need).
• trackID - an integer representing our new track
• myTracks - an array of dictionaries in the form of key "id" and value being the track ID.
• myParams - a dictionary with the key of "tracks" and the value being the aforementioned myTracks array.

So we need to turn playlist.tracks into an array of ["id":id] dictionaries with the new track ID also in there.

First, let's ignore the new track, and map the existing tracks into an array of dictionaries:

var trackIDdicts: [[String:Int]] = playlist.tracks.map { ["id":$0.id] }

And now insert our new track ID at the front:

trackIDdicts.insert(["id":trackId], atIndex:0)

And now for myParams?

myParams["playlist"] = ["tracks":trackIDdicts]

---

Altogether, three simple lines of code:

var trackIDdicts: [[String:Int]] = playlist.tracks.map { ["id":$0.id] }
trackIDdicts.insert(["id":trackId], atIndex:0)
myParams["playlist"] = ["tracks":trackIDdicts]

---

I'd highly recommend converting your JSON/Dictionary keys into named constant variables however.

struct JSONKeys {
    static let TrackID = "id"
    static let Tracks = "tracks"
    static let Playlist = "playlist"   
}

So now we have:

var trackIDdicts: [[String:Int]] = playlist.tracks.map { [JSONKeys.TrackID:$0.id] }
trackIDdicts.insert([JSONKeys.TrackID:trackId], atIndex:0)
myParams[JSONKeys.Playlist] = [JSONKeys.Tracks:trackIDdicts]