Swift 3 AWS DynamoDB json response deserialization

Question

Struggling to understand how to deserialize a json object sent from AWS DynamoDB. I'm able to successfully call dynamoDB.describeTable(describeTableInput!) and receive a detailed response ...

2017-02-08 20:30:36.054 AWS_Test[84241:3626357] AWSiOSSDK v2.5.0 [Debug] AWSURLResponseSerialization.m line:63 | -[AWSJSONResponseSerializer responseObjectForResponse:originalRequest:currentRequest:data:error:] | Response body:
{"Table":{"AttributeDefinitions":[{"AttributeName":"Author","AttributeType":"S"},{"AttributeName":"ISBN","AttributeType":"S"}],"CreationDateTime":1.486165623131E9,"GlobalSecondaryIndexes":[{"IndexArn":"arn:aws:dynamodb:ap-southeast-2:xxxxxxxxxxxxxxx:table/Books/index/ISBN-index","IndexName":"ISBN-index","IndexSizeBytes":94946,"IndexStatus":"ACTIVE","ItemCount":1780,"KeySchema":[{"AttributeName":"ISBN","KeyType":"HASH"}],"Projection":{"ProjectionType":"ALL"},"ProvisionedThroughput":{"NumberOfDecreasesToday":0,"ReadCapacityUnits":5,"WriteCapacityUnits":5}},{"IndexArn":"arn:aws:dynamodb:ap-southeast-2:xxxxxxxxxxxxxx:table/Books/index/Author-index","IndexName":"Author-index","IndexSizeBytes":94946,"IndexStatus":"ACTIVE","ItemCount":1780,"KeySchema":[{"AttributeName":"Author","KeyType":"HASH"}],"Projection":{"ProjectionType":"ALL"},"ProvisionedThroughput":{"NumberOfDecreasesToday":0,"ReadCapacityUnits":5,"WriteCapacityUnits":5}}],"ItemCount":1780,"KeySchema":[{"AttributeName":"ISBN","KeyType":"HASH"}],"ProvisionedThroughput":{"NumberOfDecreasesToday":0,"ReadCapacityUnits":5,"WriteCapacityUnits":5},"TableArn":"arn:aws:dynamodb:ap-southeast-2:xxxxxxxxxxxxxxxxx:table/Books","TableName":"Books","TableSizeBytes":94946,"TableStatus":"ACTIVE"}}

My function calling Dynamo ...

func describeTable() {

        let dynamoDB = AWSDynamoDB.default()
        let describeTableInput = AWSDynamoDBDescribeTableInput()
        describeTableInput?.tableName = "Books"

        let tableDescription = dynamoDB.describeTable(describeTableInput!) as! AWSTask<AnyObject>

        let jsonResult: NSDictionary = try JSONSerialization.JSONObjectWithData(Data, options: JSONSerialization.ReadingOptions.MutableContainers) as! NSDictionary

        print(jsonResult.object(forKey: "ItemCount")!)
        // let's dump everything to see what was returned
        dump(tableDescription)

    }

But I've been struggling for days now trying to work out how to deserialize the response and store in my own dictionary.

Anyone able to assist!? thx!

user7367181 · Accepted Answer · 2017-02-10 04:30:01Z

1

Have you tried using the SwiftyJSON library? Third party libraries will save you from a massive headache, especially when dealing with data. With it, your code will look a little like:

let json = JSON(jsonResult)
if let count = json["Table"]["GlobalSecondaryIndexes"]["ItemCount"].int {
  print(count) //your count should be accessible here
}

Remember that JSON values are nested, so simply calling json["ItemCount"] will not return what you are expecting.

answered Feb 10, 2017 at 4:30

user7367181

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jasonb202020 · Accepted Answer · 2017-02-15 10:50:26Z

After digging and screaming and digging and crying I found hints here : https://github.com/awslabs/aws-sdk-ios-samples/blob/master/DynamoDBObjectMapper-Sample/Swift/DynamoDBSampleSwift/DDBDynamoDBManager.swift

Refactoring my code got me to accessing the response values ..

func describeTable() {
        let dynamoDB = AWSDynamoDB.default()
        let describeTableInput = AWSDynamoDBDescribeTableInput()
        describeTableInput?.tableName = "Books"
        let describeTask = dynamoDB.describeTable(describeTableInput!)

        var localTask:AWSTask<AnyObject>?

        localTask = describeTask.continueOnSuccessWith(block: { task -> AnyObject? in

            let describeTableOutput:AWSDynamoDBDescribeTableOutput = task.result!
            let tableName = describeTableOutput.table!.tableName
            let tableStatus = describeTableOutput.table!.tableStatus
            let itemCount = describeTableOutput.table?.itemCount

            print("--------------------------")
            print(tableName! as String)
            if tableStatus == AWSDynamoDBTableStatus.active {
                print("Active")
            } else {
                print("Inactive")
            }
            print(itemCount as! Int)
            print("--------------------------")

            return localTask
        })
    }

Hope this helps someone else!

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