Exception: ActiveRecord::IrreversibleMigration

Inherits:

MigrationError

• Object
• StandardError
• ActiveRecordError
• MigrationError
• ActiveRecord::IrreversibleMigration

Defined in:

lib/active_record/migration.rb

Overview

Exception that can be raised to stop migrations from being rolled back. For example the following migration is not reversible. Rolling back this migration will raise an ActiveRecord::IrreversibleMigration error.

class IrreversibleMigrationExample < ActiveRecord::Migration[7.1]
  def change
    create_table :distributors do |t|
      t.string :zipcode
    end

    execute "      ALTER TABLE distributors\n        ADD CONSTRAINT zipchk\n          CHECK (char_length(zipcode) = 5) NO INHERIT;\n    SQL\n  end\nend\n"

There are two ways to mitigate this problem.

1. Define #up and #down methods instead of #change:

class ReversibleMigrationExample < ActiveRecord::Migration[7.1]
  def up
    create_table :distributors do |t|
      t.string :zipcode
    end

    execute "      ALTER TABLE distributors\n        ADD CONSTRAINT zipchk\n          CHECK (char_length(zipcode) = 5) NO INHERIT;\n    SQL\n  end\n\n  def down\n    execute <<~SQL\n      ALTER TABLE distributors\n        DROP CONSTRAINT zipchk\n    SQL\n\n    drop_table :distributors\n  end\nend\n"

1. Use the #reversible method in #change method:

class ReversibleMigrationExample < ActiveRecord::Migration[7.1]
  def change
    create_table :distributors do |t|
      t.string :zipcode
    end

    reversible do |dir|
      dir.up do
        execute "          ALTER TABLE distributors\n            ADD CONSTRAINT zipchk\n              CHECK (char_length(zipcode) = 5) NO INHERIT;\n        SQL\n      end\n\n      dir.down do\n        execute <<~SQL\n          ALTER TABLE distributors\n            DROP CONSTRAINT zipchk\n        SQL\n      end\n    end\n  end\nend\n"

Method Summary

Methods inherited from MigrationError

#initialize

Constructor Details

This class inherits a constructor from ActiveRecord::MigrationError