Reorder Rails database migrations files

November 26, 2023

On new Rails apps, that are not in production yet, I sometimes like to reorder my database migrations. I wrote a small Ruby script to automate things.

#!/usr/bin/env ruby

x = STEP = 10

Dir.entries('.').sort.each do |file|
  next unless file =~ /^[\d]+.*rb$/

  File.rename(file, format('%05<x>d_%<suffix>s', x:, suffix: file.split('_')[1..].join('_')))
  x += STEP
end

I use this Ruby script to rename files in the current directory (., which stands for the current directory) according to a specific pattern. It is aimed at Ruby files with names starting with numbers, specifically Rails database migration files. Let me break down the code a bit:

#!/usr/bin/env ruby: This is a shebang line used in Unix-based systems to tell the system to execute this script using a Ruby interpreter.

x = STEP = 10: This line initializes two variables, x and STEP, and sets them both to 10. x will be used to generate new filenames, and STEP is the increment value for x.

Dir.entries('.'): This gets all entries (files and directories) in the current directory.

.sort.each do |file|: This iterates over the sorted list of directory entries.

next unless file =~ /^[\d]+.*rb$/: This line is a guard clause. It skips to the next iteration unless the filename matches the given regular expression. The regex ^[\d]+.*rb$ matches any string that starts (^) with one or more digits ([\d]+), followed by any characters (.*), and ends with rb (indicating a Ruby file).

File.rename(...): This renames the file. The new name is generated using format, which is a method to create formatted strings.

format('%05<x>d_%<suffix>s', x:, suffix: ...: The format string '%05<x>d_%<suffix>s' creates a new filename with two parts:

• %05<x>d formats x as a zero-padded decimal integer with a width of 5 characters.
• %<suffix>s is a placeholder for the suffix of the filename, which is everything after the first underscore in the original filename.

file.split('_')[1..].join('_'): This splits the original filename at underscores, takes all parts except the first one (which is the numeric prefix), and then joins these parts back together with underscores.

x += STEP: Increments x by STEP (which is 10) for the next iteration.

This script renames all Ruby files in the current directory that start with a number. It renumbers these files starting from 10, incrementing by 10 for each file, and retains the rest of the original filename after the first underscore. For example, if there's a file named 123_example.rb, it would be renamed to 00010_example.rb. The next file would then start from 00020, and so on.

After I run this script I reset my database:

> be rails db:drop &&
  be rails db:create &&
  be rails db:migrate &&
  be rails db:migrate RAILS_ENV=test &&
  be rails db:seed

The be is a shell alias alias be='bundle exec'

rails (4) database (2)