How to create a migration to remove an index only if it exists, rather than throwing an exception if it doesn't?

Question

Right now, the current migration might fail, if the books table doesn\'t have created_at or updated_at fields:

class AddTi         


        

Answer 1

Rails 6.1+ if_exists / if_not_exists options

Rails 6.1 added if_exists option to remove_index in order to not raise an error when the index is already removed.

Rails 6.1 added if_not_exists option to add_index in order to not raise an error when the index is already added.

As a result, your migration can be rewritten in the following way:

class AddTimestampIndexes < ActiveRecord::Migration
  def up
    remove_index :books, :created_at, if_exists: true
    remove_index :books, :updated_at, if_exists: true

    add_index :books, :created_at
    add_index :books, :updated_at
  end

  def down
    remove_index :books, :created_at, if_exists: true
    remove_index :books, :updated_at, if_exists: true
  end
end

Here is a list of the links to the corresponding PRs:

• Add if_exists option to remove_index,
• Fix index options for if_not_exists/if_exists.