Getting multiple pages of results from AWS DynamoDB with iOS swift

Question

Let me preface this question by saying that I'm very new to coding with Swift and in iOS in general. I've got some experience in Java/Android and am starting to work with iOS as well now.

I need to query a dynamodb table with enough data in it that Amazon paginates the results (I think the limit is 100kb). Using the limited examples for AWS/Swift I am able to query that table but only successfully retrieve the first page of data. My question is how to get that 2nd, 3rd, etc page of data. See code below

let queryExpression = AWSDynamoDBQueryExpression()
        queryExpression.keyConditionExpression = "venue_event = :ev"
        queryExpression.expressionAttributeValues = [":ev" : "event"]

        dynamoDBObjectMapper.query(Event.self, expression: queryExpression).continueWithExecutor(AWSExecutor.mainThreadExecutor(), withBlock: {(task:AWSTask!) -> AnyObject! in
            let results = task.result as! AWSDynamoDBPaginatedOutput 
            for r in results.items{
                print (r)
            }
            return nil
        })

I've noticed that 'results' has a lastEvaluatedKey variable and loadNextPage method. However I can't seem to get either to give me the function I'm looking for

Thanks in advance for the help

beeth0ven · Accepted Answer · 2016-09-20 05:12:09Z

Simply:

var paginatedOutput: AWSDynamoDBPaginatedOutput?
...
    self.paginatedOutput = task.result as! AWSDynamoDBPaginatedOutput 
...

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCellWithIdentifier("NoSQLQueryResultCell", forIndexPath: indexPath) as! NoSQLQueryResultCell
    ...
    if (!loading) && (paginatedOutput?.lastEvaluatedKey != nil) && indexPath.section == self.results!.count - 1 {
        self.loadMoreResults()
    }
    return cell

}

func loadMoreResults() {
    loading = true
    paginatedOutput?.loadNextPageWithCompletionHandler({(error: NSError?) -> Void in
        if error != nil {
            print("Failed to load more results: \(error)")
            dispatch_async(dispatch_get_main_queue(), {
                self.showAlertWithTitle("Error", message: "Failed to load more more results: \(error?.localizedDescription)")
            })
        }
        else {
            dispatch_async(dispatch_get_main_queue(), {
                self.results!.appendContentsOf(self.paginatedOutput!.items)
                self.tableView.reloadData()
                self.loading = false
            })
        }
    })
}

You can download MobileHub Sample code:

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