Google Drive API (GTL) - Create multiple folder paths in order?

Question

I'm using the Google APIs Client Library for Objective-C (GTL) to access the Google Drive API.

According to it's Introduction to the Google APIs Client Library for Objective-C,

Query execution by the service is inherently asynchronous.

Which means when you try to create a path like: root/a/b/c, before you can create folder b, you'll have to:

1. Make sure a is created, if not, create it before b was trying to check it's parentRef.

2. Know the id of folder a so you can create b in it.

And same goes to c.

I use something like the following to get the id of a folder by name within a known parent folder id:

    // Get parentID by name "parent".

    let query = GTLQueryDrive.queryForChildrenListWithFolderId(parentID)
    query.q = "mimeType='application/vnd.google-apps.folder' and '\(parentID)' in parents and trashed=false and title='\(name)'"

    query.maxResults = 1

    GTLFileTicket = GTLDriveService.executeQuery(
        query,
        completionHandler: {(
            ticket:         GTLServiceTicket!,
            object:         AnyObject!,
            error:          NSError!) -> Void in

            // Callback
            self.GTLFileTicket = nil
            if error == nil {
                // Get the id from the object. If nil make another query to create a folder named "name" within folder "parentID".
            } else {
                // error handles here.
            }
    })

In the other part of the project, I called the above method within a for loop:

var parent = "root"
for item in array {
    createFolderIfNotExisted(item, parent: parent)
    parent = item
}

Apparently, it will fail and end up creating only the first folder as the 2nd query starts before the 1st query even finished. I googled around but didn't see a way to make it synchronous calls instead. (Tho I saw Java API branch can have something like .await()?)

Is there a way to make sure the calls can be executed in sequence?

Answer 1

Avoid using a synchronous for loop. The createFolder function should call back when it's complete; that callback should start the next loop iteration.