How do I save dictionary (map object) to DynamoDB using Swift - ios

Question

I’m trying to save a dictionary to my DynamoDB table field using low-level API. I couldn’t figure out how to do it with object mapper. There is no example for this in AWS iOS documentation and I’ve tried to research and implement Java / .NET examples of the same subject unsuccessfully.
I want to update only the dictionary field in the row using updateExpression.
I stumbled to this question while searching for answer, but it didn't help: Best way to make Amazon AWS DynamoDB queries using Swift?
Here’s the function to update dynamoDB-table:
func saveMapToDatabase(hashKey:Int, rangeKey:Double, myDict:[Int:Double]){
let nsDict:NSDictionary = NSDictionary(dictionary: myDict)
var dictAsAwsValue = AWSDynamoDBAttributeValue();dictAsAwsValue.M = nsDict as [NSObject : AnyObject]
let updateInput:AWSDynamoDBUpdateItemInput = AWSDynamoDBUpdateItemInput()
let hashKeyValue:AWSDynamoDBAttributeValue = AWSDynamoDBAttributeValue();hashKeyValue.N = String(hashKey)
let rangeKeyValue:AWSDynamoDBAttributeValue = AWSDynamoDBAttributeValue(); rangeKeyValue.N = String(stringInterpolationSegment: rangeKey)
updateInput.tableName = "my_table_name"
updateInput.key = ["db_hash_key" :hashKeyValue, "db_range_key":rangeKeyValue]
//How I usually do low-level update:
//let valueUpdate:AWSDynamoDBAttributeValueUpdate = AWSDynamoDBAttributeValueUpdate()
//valueUpdate.value = dictAsAwsValue
//valueUpdate.action = AWSDynamoDBAttributeAction.Put
//updateInput.attributeUpdates = ["db_dictionary_field":valueUpdate]
//Using the recommended way: updateExpression
updateInput.expressionAttributeValues = ["dictionary_value":dictAsAwsValue]
updateInput.updateExpression = "SET db_dictionary_field = :dictionary_value"
self.dynamoDB.updateItem(updateInput).continueWithBlock{(task:BFTask!)->AnyObject! in
//do some debug stuff
println(updateInput.aws_properties())
println(task.description)
return nil
}
}

Answer 1

I solved it, the problem was that AWS requires dictionary keys to always be in the form of String, any other type is not allowed.
The working solution snippet:
...
updateInput.tableName = "my_table_name"
updateInput.key = ["db_hash_key" :hashKeyValue, "db_range_key":rangeKeyValue]
let dictionaryInRightFormat:NSDictionary = ["stringKey":dictAsAwsValue]
updateInput.expressionAttributeValues = updateInput.updateExpression = "SET db_dictionary_field = :stringKey"