Don't Forget to Cast Your Boolean ENV Variables

TL;DR

# bad
if ENV.fetch('MY_VAR', false)

# good
if ActiveModel::Type::Boolean.new.cast(ENV.fetch('MY_VAR', false))

Environment variables are always strings. When using ENV variables to represent booleans, they should always be parsed as such to prevent bugs. Otherwise, you might end up accidentally writing if "false", which is truthy.

The other day, I was working on a client’s project to repair records that were missing some of their file attachments. While looking through the code, I came across this conditional:

if ENV.fetch('IMPORT_SKIP_EXISTING', false)
  # Skip processing this record's files
else
  # Process this record completely, including files
end

In case you’re unfamiliar with Ruby, ENV is a hash table of key-value pairs. The #fetch method will attempt to fetch the value at the specified key, i.e. the first argument ("IMPORT_SKIP_EXISTING"). If a value can’t be found, it falls back on the second argument (false)

One way to repair the broken records is to reimport them into the database, effectively syncing them with the data’s source of truth. I chose this as my path forward and checked the value of the variable in the .env file:

IMPORT_SKIP_EXISTING=true

The next step was simple: change the ENV variable’s value to false to allow for each record’s files to be brought in when reimporting them.

Except… when I made the change and started reimporting, none of the records were getting any files.

What did I miss?

I was digging through the code for several minutes before I remembered:

Oh yeah, ENV variable values are strings

If we strip away the ENV fetching syntax, this is what I thought I was doing:

if false # falsy

But in reality, what I was doing was:

if "false" # truthy

The insidious part about this is that, before I changed the value, it was “working” just fine; if true and if "true" are both truthy.

The solution I chose was to cast the value to a boolean:

if ActiveModel::Type::Boolean.new.cast(ENV.fetch('IMPORT_SKIP_EXISTING', false))

Alternatively, I could have used string comparison (if "true" == "true"). However, I prefer casting to a boolean in this case since the intended purpose is an on/off switch, a.k.a. a boolean’s sole purpose.

TL;DR#

TL;DR