rails 迁移在本地 Postgresql 上运行，但在 prod 上失败

Question

简而言之，在本地 Postgres 实例上删除、创建和运行 migrate 可以多次为我的应用程序创建工作数据库，但 Heroku 产品上的相同技术总是会产生：

heroku run rake db:migrate
Running `rake db:migrate` attached to terminal... up, run.9674
PG::UndefinedTable: ERROR:  relation "mytable" does not exist
LINE 5:                WHERE a.attrelid = '"mytable"'::regclass
                                          ^
:               SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                     pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod
                FROM pg_attribute a LEFT JOIN pg_attrdef d
                  ON a.attrelid = d.adrelid AND a.attnum = d.adnum
               WHERE a.attrelid = '"mytable"'::regclass
                 AND a.attnum > 0 AND NOT a.attisdropped
               ORDER BY a.attnum

rake aborted!
PG::UndefinedTable: ERROR:  relation "mytable" does not exist
LINE 5:                WHERE a.attrelid = '"mytable"'::regclass
                                          ^
:               SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                     pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod
                FROM pg_attribute a LEFT JOIN pg_attrdef d
                  ON a.attrelid = d.adrelid AND a.attnum = d.adnum
               WHERE a.attrelid = '"mytable"'::regclass
                 AND a.attnum > 0 AND NOT a.attisdropped
               ORDER BY a.attnum

编辑：请参阅问题底部以获取有关在迁移期间访问控制器的线索。

这在本地有效：

rake db:drop
rake db:create
rake db:migrate

我有

• 通过heroku pg:psql 和\dt 确认 Heroku 的数据库在迁移前是空白的，以验证 0 个表是否存在。
• 在迁移之前尝试heroku pg:reset DATABASE
• 确认本地和生产 Postgres 是 9.2.4 版
• 尝试将db/migrate 中的“mytable”迁移文件重命名为具有最早的时间戳以便首先运行

这是一个非常简单的应用程序，因此从头开始创建数据库之类的基本操作总是失败，这非常令人沮丧。有什么想法吗？

“mytable”迁移：

class CreateMytable < ActiveRecord::Migration
  def change
    create_table :mytable do |t|
      t.string :codes
      t.string :name

      t.timestamps
    end
  end
end

可能涉及迁移：

class CreateTable2 < ActiveRecord::Migration
  def change
    create_table :table2 do |t|
      t.references :a, index: true
      t.references :b, index: true
      t.string :c
      t.string :d

      t.timestamps
    end
  end
end

编辑：使用 --trace 运行 db:migrate 时发现了一条线索。错误堆栈跟踪的顶部显示控制器错误？为什么控制器要参与迁移？

/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:768:in `exec'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:768:in `exec_no_cache'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:138:in `block in exec_query'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:425:in `block in log'
/app/vendor/bundle/ruby/2.0.0/gems/activesupport-4.0.0/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/abstract_adapter.rb:420:in `log'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:137:in `exec_query'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql_adapter.rb:915:in `column_definitions'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/postgresql/schema_statements.rb:174:in `columns'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:114:in `block in prepare_default_proc'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:56:in `yield'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/connection_adapters/schema_cache.rb:56:in `columns'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/model_schema.rb:208:in `columns'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/model_schema.rb:242:in `column_defaults'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/locking/optimistic.rb:169:in `column_defaults'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/core.rb:181:in `initialize'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/inheritance.rb:27:in `new'
/app/vendor/bundle/ruby/2.0.0/gems/activerecord-4.0.0/lib/active_record/inheritance.rb:27:in `new'
/app/app/controllers/home_controller.rb:7:in `<class:HomeController>'

有问题的第 7 行包含对 Mytable.new(... 的调用。在 db:migrate 期间控制器代码是如何进入范围的？

Answer 1

这是由于在 Rails 控制器中设置了一个引用“mytable”类的类变量造成的。所以基本上是这样的：

 class HomeController < ApplicationController
  @@data = {MyTable.new(...

将它移到控制器方法中并使其成为非类变量解决了问题（我没有区分是类 var 方面还是类 def 正下方的位置是原因）。

我仍然不明白为什么控制器代码是数据库迁移的一个因素。我很想知道这是我做错了什么，还是 rake、rails 或其他东西中的错误。只发生在 Heroku 生产，Rails 4.0.0