Adhoc Exports on Heroku's Console
Posted on March 29, 2016 by Carsten Zimmermann
Ever had that »can you give me a list of … real quick?« request coming in?
Most of the time, delivering that list only involves firing a simple Arel query
on the rails console, Array#join the record’s relevant attributes with a
mere ; and hand it over as a CSV file.
The annoying part is capturing the output: For a large resultset, it can very well exceed your terminal’s output buffer size. Even if it does fits, copy/pasting everything with your mouse is tedious at best.
Writing to a CSV file on Heroku’s Rails console requires uploading it somewhere, S3 in our case, meaning you’ll have to deal with authentication keys and APIs that I don’t know by heart. Also not my idea of quickly running a simple export.
Creating a rake task that handles everything is certainly the proper way to go,
but it means doing a git commit, waiting for the stuff to deploy and potentially
git revert the exporter again if it’s just throw-away code.
I want to stick with a simple Ruby one-liner and this is how I use the rails
runner command, invoked through the Heroku console, together with output
redirection to create my CSV file freshly from production data:
heroku run rails runner \
"puts MyModel.where(foo: 'bar').pluck(:id, :email).map { |data| data.join(';') }" \
-r production > my_adhoc_export.csv
If you want to see what’s going on while your export does its thing, use tee(1):
heroku run rails runner \
"puts 'They are going to take me away haha!'"
-r production |tee funny_farm.txt
Now, a bit of an advise: running code on your production system is not a Good Idea™. If you have to run anything more complex than a simple query-command, wrap it into a rake task (or some such). The above example is meant for one-off tasks that output stuff to my local terminal. You have been warned :)