Last month I learnt - ruby can be weird

I was working on a task that involved parsing data from CSV files and saving it into rails models when I noticed something that didn’t look right. On calling to_json on one of the parsed csv rows, I got;

{
  "": null,
  "name": "John"
}

For context, I was parsing the CSV using the headers: true option, and for some reason, I had an empty header. Since we all know that developers don’t make mistakes, it had to be an issue with the data. So, I went hunting.

Another lesson, if you’re looking for an issue with data, open it in it’s raw form. Opening the csv with LibreOffice Calc and choosing the helpful defaults, opened a perfectly good sheet, and surprise, no missing header! Just as I was about to concede that it might be me, I opened the file in my editor(vim) and despite the ugliness, the trailing comma on each line was hard to miss.

With a possible culprit found, it was back to the code to try and get rid of that entry. Q; which ruby type would result in an empty string in json? Now, if you use ruby I’d assume there’s literally no time you’ve wanted to use an empty string as a key in your hash, right? But still it get’s weirder, on calling to_h on the row;

{
  nil => nil,
  "name" => "John"
}

What?! Yes, nil is a valid key in a ruby hash. I had to fire up plain irb to make sure it wasn’t rails messsing with me. And just to be sure, I confirmed that it’s also possible to retrieve the value normally with hsh[nil]

P.S If you ever find yourself needing to read json exported from mongo, BSON::ExtJSON.parse is your friend.

Comments

[Paweł Świątkowski]

Well you can use any object as the key in the hash. Including nil, other hash or ActiveRecord object ;) That wouldn't be very performant, but it's technically possible.