ruby-on-rails - 迁移不回滚

Question

我已经运行了这个迁移:

class AddUniqueToLocationColumnName < ActiveRecord::Migration
  def change
    remove_index :locations, :name
    add_index :locations, :name, unique: true
  end
end

现在我正在尝试回滚，但显示错误:

StandardError: An error has occurred, this and all later migrationscanceled: remove_index is only reversible if given a :column option.

如何将此迁移回滚到我以前的版本？

Answer 1

尝试明确定义 up 和 down:

class AddUniqueToLocationColumnName < ActiveRecord::Migration
  def self.up
    remove_index :locations, column: :name
    add_index :locations, :name, unique: true
  end

  def self.down
    remove_index :locations, column: :name # remove unique index
    add_index :locations, :name # adds just index, without unique
  end
end