db：schema：load vs db：使用capistrano迁移

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问题描述

我有一个rails应用程序，我移动到另一个服务器，我想我应该使用db：schema：load创建mysql数据库，因为它是建议。我的问题是，我使用capistrano部署，它似乎是默认的rake db：migrate。有没有办法改变这个或者是capistrano使用db：migrate有很好的理由？

I have a rails app that I'm moving to another server and I figure I should use db:schema:load to create the mysql database because it's recommended. My problem is that I'm using capistrano to deploy and it seems to be defaulting to rake db:migrate instead. Is there a way to change this or is capistrano using db:migrate for a good reason?

：load

我发现我自己的迁移最终会做一些数据混洗（假设我将first_name和last_name列合并成一个full_name列）。一旦我做任何这些，我开始使用ActiveRecord筛选数据库记录，你的模型最终做出关于某些列的假设。例如，我的Person表，后来被赋予了一个位置列，人们被排序。

Why to use db:schema:load

I find that my own migrations eventually do some shuffling of data (suppose I combine first_name and last_name columns into a full_name column, for instance). As soon as I do any of this, I start using ActiveRecord to sift through database records, and your models eventually make assumptions about certain columns. My "Person" table, for instance, was later given a "position" column by which people are sorted. Earlier migrations now fail to select data, because the "position" column doesn't exist yet.

总之，我相信 deploy：cold 应该使用 db：schema：load 而不是 db：migrate 。我通过改变中间的步骤解决这个问题，Capistrano在冷部署执行。对于Capistrano v2.5.9，库代码中的默认任务看起来像这样。

In conclusion, I believe deploy:cold should use db:schema:load instead of db:migrate. I solved this problem by changing the middle step which Capistrano performs on a cold deploy. For Capistrano v2.5.9, the default task in the library code looks like this.

namespace :deploy do
  ...
  task :cold do
    update
    migrate  # This step performs `rake db:migrate`.
    start
  end
  ...
end

我重写了我的 deploy.rb 中的任务如下。

I overrode the task in my deploy.rb as follows.

namespace :deploy do
  task :cold do       # Overriding the default deploy:cold
    update
    load_schema       # My own step, replacing migrations.
    start
  end

  task :load_schema, :roles => :app do
    run "cd #{current_path}; rake db:schema:load"
  end
end

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cold