如何使用 Swift 将字典（地图对象）保存到 DynamoDB

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"