How to extract integer from list with tuple in Elixir?

Question

I'm trying to get a count from an ODBC database in Elixir. I can see my result coming back, however, I don't know how to extract the value.

{:ok, conn} = :odbc.connect('DSN=mydsn;UID=myuid;PWD=mypwd', [])
{:selected, _colNames, rows} = :odbc.sql_query(conn, 'select count(*) from mytable')

{:selected, ['COUNT'], [{'182'}]}

How do I get 182 out as an integer?

The closest I got was getting the inner tuple:

hd(rows)

{'182'}

Answer 1

There are different possible solutions depending whether you are interested in this specific case or in a broader approach.

In this specific instance, as rows is expected to be a list with a single tuple with a single value, you can take advantage of the pattern matching to extract the value.

{:selected, _, [{count}]} = {:selected, ['COUNT'], [{'182'}]}

From this point count will match '182'. However, please note that '182' is different than "182"

"182" == '182'
false

As explained in the Elixir documentation, '182' is a char-list whereas "182" is a String. Therefore you can't use String.to_integer directly as it will fail.

String.to_integer(count)
** (ArgumentError) argument error
    :erlang.binary_to_integer('182')

You first need to use List.to_integer(count) or alternatively convert it into a String, then cast to an integer.

List.to_integer(count)
182

String.to_integer(to_string(count))
182

This solution may not be applicable directly if the tuple contains more than one value (which means the query returns more than one value as result). However it's a starting point you can adapt to your needs.