query() function from dynamodb()

[jtruffa]

Hi,
query() returns me a nested list.
in the Items sections, every attribute of a record is itself a list.

` $ :List of 9
  ..$ version     :List of 10
  .. ..$ S   : chr "1"
  .. ..$ N   : chr(0) 
  .. ..$ B   : chr(0) 
  .. ..$ SS  : list()
  .. ..$ NS  : list()
  .. ..$ BS  : list()
  .. ..$ M   : list()
  .. ..$ L   : list()
  .. ..$ NULL: logi(0) 
  .. ..$ BOOL: logi(0) `

Is there any way of telling query() to return just the attribute with its corresponding value?

I couln't find it in the doc.

thanks,

[davidkretch]

Sorry about that. Unfortunately there isn't anything built in -- Paws doesn't do anything extra with what DynamoDB returns, at least at the moment.

However, I put together the flatten function below which may help. It will flatten your list to show only the attribute names and values.

# Example DynamoDB result data.
a <- list(
  Foo = list(
    S = character(0),
    N = list(),
    B = list(),
    L = list(),
    M = list(
      Bar = list(
        S = "1",
        N = list(),
        B = list(),
        L = list(),
        M = list()
      )
    )
  )
)

# Flatten a DynamoDB query response, into an object that has only attribute names and values. 
flatten <- function(x) {
  result <- list()
  for (name in names(x)) {
    result[[name]] <- get_value(x[[name]])
  }
  return(result)
}

# Get the value from a single attribute.
get_value <- function(x) {
  element <- names(x)[sapply(x, function(el) length(el) > 0)]
  if (element == "M") return(flatten(x[[element]]))
  return(x[[element]])
}

# Test the flatten function on the example data.
b <- flatten(a)

# > str(b)
# List of 1
#  $ Foo:List of 1
#   ..$ Bar: chr "1"

[jmtruffa]

Hi David,
Thanks for the solution you have provided!
With a little tweak, since the response that I got has one more level, I finally obtained a more usable list (put it in a for loop)

Don't know why dynamo returns the full list of data types like this.

You can close the issue.
Great work!

[davidkretch]

Awesome! Glad to hear it.

My guess about that response shape is I think it's designed for languages that have fixed data types, so they have a slot for strings, for integers, etc.

Thanks for bringing it up. This is a good example and if I get some time, I'll put it in the examples folder too.

Have a good one!