将 HStore 列更改为数组

Question

我的 Rails/Postgres 应用程序中有一个列，我想将其从 Hstore 更改为 Array。 （我将手机存储为哈希，所以我可以使用{default: 123, mobile: 1234}，但我认为它没有必要/没用）

所以我做了以下迁移：

class ChangePhonesToArray < ActiveRecord::Migration
  def up
    new_phones = {}
    Place.find_each do |p|
      new_phones[p.id] = p.phones.values.map{ |v| v.gsub(%r!\D!, '') } # get rid of non-number characters while I'm at it
    end

    remove_column :places, :phones

    add_column :places, :phones, :string, array: true, default: []

    new_phones.each do |k, v|
      p = Place.find(k)
      p.update_attributes!(phones: v)
    end
  end
  ...
end

但是，当我这样做时，我得到了这个令人讨厌的 DB 错误，表明 phones 仍然是一个 Hstore 列！

StandardError: An error has occurred, this and all later migrations canceled:

can't cast Array to hstore/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/abstract/quoting.rb:76:in `type_cast'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql/quoting.rb:111:in `type_cast'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql_adapter.rb:828:in `block in exec_cache'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql_adapter.rb:827:in `map'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql_adapter.rb:827:in `exec_cache'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `exec_delete'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/abstract/database_statements.rb:101:in `update'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/abstract/query_cache.rb:14:in `update'

我认为该列没有被正确删除，所以我在第一个之后立即在其中扔了第二个remove_column，这引发了以下错误，表明该列已被删除！ （但显然不完全）。

StandardError: An error has occurred, this and all later migrations canceled:

PG::UndefinedColumn: ERROR:  column "phones" of relation "places" does not exist
: ALTER TABLE "places" DROP "phones"/Users/sasha/.rvm/gems/ruby-2.1.2/gems/rack-mini-profiler-0.9.2/lib/patches/sql_patches.rb:160:in `exec'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/rack-mini-profiler-0.9.2/lib/patches/sql_patches.rb:160:in `async_exec'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql/database_statements.rb:128:in `block in execute'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/abstract_adapter.rb:373:in `block in log'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activesupport-4.1.4/lib/active_support/notifications/instrumenter.rb:20:in `instrument'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/abstract_adapter.rb:367:in `log'
/Users/sasha/.rvm/gems/ruby-2.1.2/gems/activerecord-4.1.4/lib/active_record/connection_adapters/postgresql/database_statements.rb:127:in `execute'

知道这里发生了什么，以及如何修复/解决它吗？

Answer 1

仅仅因为您更改了数据库中的表架构并不意味着您的Place 类知道这些更改。 ActiveRecord::Base 子类只加载一次列信息，以避免不必要地一遍又一遍地访问数据库。只要你这样做：

Place.find_each

您的Place 将知道列类型是什么。然后更改Place 背后的模式并尝试写入新值，但Place 不知道这些更改。通常的解决方法是致电reset_column_information:

重置有关列的所有缓存信息，这将导致它们在下一次请求时重新加载。

此方法最常见的使用模式可能是在迁移中...

所以你会说：

#...
remove_column :places, :phones
add_column :places, :phones, :string, array: true, default: []
Place.reset_column_information
#...

顺便说一句，不能保证hstore 会保持任何顺序，因此您可能需要p.phones.values_at(:default, :mobile) 而不是p.phones.values 以确保数组中的顺序正确。