Module: ActiveRecord::Migration::Compatibility

Defined in:
lib/active_record/migration/compatibility.rb

Overview

:nodoc: all

Defined Under Namespace

Classes: V4_2, V5_0, V5_1, V5_2, V6_0, V6_1, V7_0, V7_1

Constant Summary collapse

V7_2 =

This file exists to ensure that old migrations run the same way they did before a Rails upgrade. e.g. if you write a migration on Rails 6.1, then upgrade to Rails 7, the migration should do the same thing to your database as it did when you were running Rails 6.1

“Current” is an alias for ‘ActiveRecord::Migration`, it represents the current Rails version. New migration functionality that will never be backward compatible should be added directly to `ActiveRecord::Migration`.

There are classes for each prior Rails version. Each class descends from the next Rails version, so: 5.2 < 6.0 < 6.1 < 7.0 < 7.1 < 7.2

If you are introducing new migration functionality that should only apply from Rails 7 onward, then you should find the class that immediately precedes it (6.1), and override the relevant migration methods to undo your changes.

For example, Rails 6 added a default value for the ‘precision` option on datetime columns. So in this file, the `V5_2` class sets the value of `precision` to `nil` if it’s not explicitly provided. This way, the default value will not apply for migrations written for 5.2, but will for migrations written for 6.0.

Current

Class Method Summary collapse

Class Method Details

.find(version) ⇒ Object 



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# File 'lib/active_record/migration/compatibility.rb', line 6

def self.find(version)
  version = version.to_s
  name = "V#{version.tr('.', '_')}"
  unless const_defined?(name)
    versions = constants.grep(/\AV[0-9_]+\z/).map { |s| s.to_s.delete("V").tr("_", ".").inspect }
    raise ArgumentError, "Unknown migration version #{version.inspect}; expected one of #{versions.sort.join(', ')}"
  end
  const_get(name)
end