Facebook iOS SDK & Swift - How do I create dependent batch requests?

Question

I'm trying to figure out how to compose FB Graph API requests (FB SDK 4.0 and Swift) when the second (child) request is dependent on the first (parent) request. Specifically I would like to get a user's albums and each album's cover photo.

1. me/albums?fields=name,cover_photo <-- Get user albums request

2. /888474748 <-- Get cover photo request

The documentation is very vague regarding this and API docs for FBSDKGraphRequestConnection mention that method addRequest:completionHandler:batchParameters: can accept parameters such as "name" and "depends_on". This appears to be the method I'm looking for but I can find an example of its use in Obj-C or Swift.

Should it look something like this? Thanks!

 let albumRequest = FBSDKGraphRequest(graphPath: "me/albums?fields=name,cover_photo", parameters: nil)
    let albumCoverRequest = FBSDKGraphRequest(graphPath: "cover_photo_id", parameters: nil) //what should this look like? jsonpath?
    let graphConnection = FBSDKGraphRequestConnection()
    graphConnection.addRequest(albumRequest, completionHandler: { (connection:FBSDKGraphRequestConnection!, result:AnyObject!, error:NSError!) -> Void in
        if(error != nil){
            println(error)
        }else{

        }
        },batchParameters: ["name" : "albums"])

    graphConnection.addRequest(albumRequest, completionHandler: { (connection:FBSDKGraphRequestConnection!, result:AnyObject!, error:NSError!) -> Void in
        if(error != nil){
            println(error)
        }else{

        }
        },batchParameters: ["depends_on" : "albums"]) //should this be some jsonpath expression?

Answer 1

Got it figured out.

let albumRequest = FBSDKGraphRequest(graphPath: "me/albums?fields=name,cover_photo", parameters: nil)
    let albumCoverRequest = FBSDKGraphRequest(graphPath: "?ids={result=albums:$.data.*.cover_photo}", parameters: nil) // use jsonpath syntax to "inject" parent results into "child" request
    let graphConnection = FBSDKGraphRequestConnection()
    graphConnection.addRequest(albumRequest, completionHandler: { (connection:FBSDKGraphRequestConnection!, result:AnyObject!, error:NSError!) -> Void in
        if(error != nil){
            println(error)
        }else{
            println(result)
        }
        },batchParameters: ["name" : "albums"]) //Set "parent" batch alias

    graphConnection.addRequest(albumCoverRequest, completionHandler: { (connection:FBSDKGraphRequestConnection!, result:AnyObject!, error:NSError!) -> Void in
        if(error != nil){
            println(error)
        }else{
            println(result)
        }
        },batchParameters: ["depends_on" : "albums"]) //depend on parent batch alias
    graphConnection.start()