Sooner or later, in a Ruby on Rails application, the db/migrations directory tends to pile up with obsolete, unused migrations.

The best way I found to squash them into one file and move on is to:

• Backup all the db/migrations directory, somewhere outside the project or don’t forget to add it to .gitgnore If you decide to keep it inside of it
• Create a new Rails migration e.g. rails g migration squash_v1
• Copy the contents of db/schema.rb file inside the ActiveRecord::Schema.define(version: xxxxyyyyzzzz) do block
• Open the db/migrations/xxxxxxxxxxxx_squash_v1.rb file and paste inside the block

  class SquashMigrationV1 < ActiveRecord::Migration[6.1]
  def change
  ....
  

– Done –