Rails迁移已删除关联表中的条目

Question

In rails (2.3.5) I have 2 associated models:

class Report < ActiveRecord::Base
  has_many :studys, :dependent => :destroy
end

class Study < ActiveRecord::Base
  validates_presence_of :name, :report_id
  belongs_to :report
end

I'm running a migration on the reports table:

class AddReportUsername< ActiveRecord::Migration

def self.up
  add_column :reports, :username, :text, :limit => 20
end

This migration deletes all entries in my studies table.

My assumption is that the ALTER TABLE command invoked by the add_column deletes the reports table and recreate it with the new column. Because of the association between the Study and Report models, the dependent studies are destroyed.

If this is true - is there a way to prevent Rails from doing that? Or, can someone explain why this is happening?

Answer 1

您的模型很好，迁移对我来说很好，所以我最好的猜测是您没有使用正确的命令...您是在使用普通的旧rake db:migrate还是更高级的工具？