def ddl_transaction(&block)
  if Base.connection.supports_ddl_transactions?
    Base.transaction { block.call }
  else
    block.call
  end
end

正如你可以看到的,如果连接支持它,它会将迁移包装在一个事务中.

在ActiveRecord :: ConnectionAdapters :: PostgresqlAdapter你有：

def supports_ddl_transactions?
  true
end

sqlite 2.0及更高版本也支持迁移事务.
在ActiveRecord :: ConnectionAdapters :: sqliteAdapter你有：

def supports_ddl_transactions?
  sqlite_version >= '2.0.0'
end

那么,为了跳过交易,你需​​要以某种方式规避这一点.
这样的事情可能会起作用,虽然我还没有测试过：

class ActiveRecord::Migration
  class << self
    def no_transaction
      @no_transaction = true
    end
 
    def no_transaction?
      @no_transaction == true
    end
  end
 
  private
 
    def ddl_transaction(&block)
      if Base.connection.supports_ddl_transactions? && !self.class.no_transaction?
        Base.transaction { block.call }
      else
        block.call
      end
    end
end

然后,您可以按如下方式设置迁移：

class SomeMigration < ActiveRecord::Migration
  no_transaction
 
  def self.up
    # Do something
  end
 
  def self.down
    # Do something
  end
end