ruby-on-rails - 将 HStore 列更改为数组

Question

我想将我的 Rails/Postgres 应用程序中的一列从 Hstore 更改为数组。 (我将电话存储为散列，所以我可以做 {default: 123, mobile: 1234}，但我认为这没有必要/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

然而，当我这样做时，我得到了这个讨厌的数据库错误，提示 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'

我假设该列没有被正确删除，所以我在第一个之后立即在其中添加了第二个 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/绕过它吗？

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 子类只加载列信息一次，以避免不必要地一遍又一遍地访问数据库。一旦你这样做:

Place.find_each

您的 Place 将知道列类型是什么。然后，您更改 Place 背后的架构并尝试写入新值，但 Place 不知道这些更改。通常的解决方法是调用 reset_column_information :

Resets all the cached information about columns, which will cause them to be reloaded on the next request.

The most common usage pattern for this method is probably in a migration...

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，因此您可能希望 p.phones.values_at(:default, :mobile) 而不是 p.phones.values 以确保事物在数组中的顺序正确。