我面临以下问题：我在Postgresql中使用Rails 4。我使用了称为hstore的强大功能，用于在数据库中存储键/值对的集合。
记录示例：
<Category id: 2, name: "Phone",..., additional_fields: {"ram"=>"2gb", "camera"=>"8mp"}>
> Category.find(2).additional_fields.class
=> Hash
但是在我的视图内（甚至在控制器内），它转换为String！
<% @category.additional_fields.class %> # returns String
控制器：
def set_category
@category = Category.find(params[:id])
end
由于下一段代码导致错误
<% @category.additional_fields.each do |key, value| %>
<div class="form-group">
<%= text_field_tag key, key %>
...
<% end %>
未定义方法'each'for“ \” ram \“ => \” 2gb \“，\” camera \“ => \” 8mp \“” ：String
完整跟踪：
app/views/categories/_form.html.erb:21:in `block (2 levels) in _app_views_categories__form_html_erb__671254231_94341970'
actionpack (4.0.0) lib/action_view/helpers/capture_helper.rb:38:in `block in capture'
actionpack (4.0.0) lib/action_view/helpers/capture_helper.rb:200:in `with_output_buffer'
actionpack (4.0.0) lib/action_view/helpers/capture_helper.rb:38:in `capture'
actionpack (4.0.0) lib/action_view/helpers/form_helper.rb:699:in `fields_for'
actionpack (4.0.0) lib/action_view/helpers/form_helper.rb:1538:in `fields_for'
app/views/categories/_form.html.erb:20:in `block in _app_views_categories__form_html_erb__671254231_94341970'
actionpack (4.0.0) lib/action_view/helpers/capture_helper.rb:38:in `block in capture'
actionpack (4.0.0) lib/action_view/helpers/capture_helper.rb:200:in `with_output_buffer'
actionpack (4.0.0) lib/action_view/helpers/capture_helper.rb:38:in `capture'
actionpack (4.0.0) lib/action_view/helpers/form_helper.rb:435:in `form_for'
app/views/categories/_form.html.erb:1:in `_app_views_categories__form_html_erb__671254231_94341970'
actionpack (4.0.0) lib/action_view/template.rb:143:in `block in render'
activesupport (4.0.0) lib/active_support/notifications.rb:161:in `instrument'
actionpack (4.0.0) lib/action_view/template.rb:141:in `render'
actionpack (4.0.0) lib/action_view/renderer/partial_renderer.rb:306:in `render_partial'
actionpack (4.0.0) lib/action_view/renderer/partial_renderer.rb:279:in `block in render'
actionpack (4.0.0) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.0) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (4.0.0) lib/action_view/renderer/partial_renderer.rb:278:in `render'
actionpack (4.0.0) lib/action_view/renderer/renderer.rb:47:in `render_partial'
actionpack (4.0.0) lib/action_view/helpers/rendering_helper.rb:27:in `render'
app/views/categories/edit.html.erb:3:in `_app_views_categories_edit_html_erb___781726467_94347130'
actionpack (4.0.0) lib/action_view/template.rb:143:in `block in render'
activesupport (4.0.0) lib/active_support/notifications.rb:161:in `instrument'
actionpack (4.0.0) lib/action_view/template.rb:141:in `render'
actionpack (4.0.0) lib/action_view/renderer/template_renderer.rb:49:in `block (2 levels) in render_template'
actionpack (4.0.0) lib/action_view/renderer/abstract_renderer.rb:38:in `block in instrument'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.0) lib/action_view/renderer/abstract_renderer.rb:38:in `instrument'
actionpack (4.0.0) lib/action_view/renderer/template_renderer.rb:48:in `block in render_template'
actionpack (4.0.0) lib/action_view/renderer/template_renderer.rb:56:in `render_with_layout'
actionpack (4.0.0) lib/action_view/renderer/template_renderer.rb:47:in `render_template'
actionpack (4.0.0) lib/action_view/renderer/template_renderer.rb:17:in `render'
actionpack (4.0.0) lib/action_view/renderer/renderer.rb:42:in `render_template'
actionpack (4.0.0) lib/action_view/renderer/renderer.rb:23:in `render'
actionpack (4.0.0) lib/abstract_controller/rendering.rb:127:in `_render_template'
actionpack (4.0.0) lib/action_controller/metal/streaming.rb:219:in `_render_template'
actionpack (4.0.0) lib/abstract_controller/rendering.rb:120:in `render_to_body'
actionpack (4.0.0) lib/action_controller/metal/rendering.rb:33:in `render_to_body'
actionpack (4.0.0) lib/action_controller/metal/renderers.rb:26:in `render_to_body'
actionpack (4.0.0) lib/abstract_controller/rendering.rb:97:in `render'
actionpack (4.0.0) lib/action_controller/metal/rendering.rb:16:in `render'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:41:in `block (2 levels) in render'
activesupport (4.0.0) lib/active_support/core_ext/benchmark.rb:12:in `block in ms'
/home/mike/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/benchmark.rb:296:in `realtime'
activesupport (4.0.0) lib/active_support/core_ext/benchmark.rb:12:in `ms'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:41:in `block in render'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:84:in `cleanup_view_runtime'
activerecord (4.0.0) lib/active_record/railties/controller_runtime.rb:25:in `cleanup_view_runtime'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:40:in `render'
actionpack (4.0.0) lib/action_controller/metal/implicit_render.rb:10:in `default_render'
actionpack (4.0.0) lib/action_controller/metal/implicit_render.rb:5:in `send_action'
actionpack (4.0.0) lib/abstract_controller/base.rb:189:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.0.0) lib/abstract_controller/callbacks.rb:18:in `block in process_action'
activesupport (4.0.0) lib/active_support/callbacks.rb:413:in `_run__967049018__process_action__callbacks'
activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.0) lib/abstract_controller/callbacks.rb:17:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `block in instrument'
activesupport (4.0.0) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.0.0) lib/active_support/notifications.rb:159:in `instrument'
actionpack (4.0.0) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.0.0) lib/action_controller/metal/params_wrapper.rb:245:in `process_action'
activerecord (4.0.0) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.0.0) lib/abstract_controller/base.rb:136:in `process'
actionpack (4.0.0) lib/abstract_controller/rendering.rb:44:in `process'
actionpack (4.0.0) lib/action_controller/metal.rb:195:in `dispatch'
actionpack (4.0.0) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.0.0) lib/action_controller/metal.rb:231:in `block in action'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:80:in `call'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:80:in `dispatch'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:48:in `call'
actionpack (4.0.0) lib/action_dispatch/journey/router.rb:71:in `block in call'
actionpack (4.0.0) lib/action_dispatch/journey/router.rb:59:in `each'
actionpack (4.0.0) lib/action_dispatch/journey/router.rb:59:in `call'
actionpack (4.0.0) lib/action_dispatch/routing/route_set.rb:655:in `call'
warden (1.2.3) lib/warden/manager.rb:35:in `block in call'
warden (1.2.3) lib/warden/manager.rb:34:in `catch'
warden (1.2.3) lib/warden/manager.rb:34:in `call'
rack (1.5.2) lib/rack/etag.rb:23:in `call'
rack (1.5.2) lib/rack/conditionalget.rb:25:in `call'
rack (1.5.2) lib/rack/head.rb:11:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/flash.rb:241:in `call'
rack (1.5.2) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.5.2) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/cookies.rb:486:in `call'
activerecord (4.0.0) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.0.0) lib/active_record/connection_adapters/abstract/connection_pool.rb:626:in `call'
activerecord (4.0.0) lib/active_record/migration.rb:369:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.0.0) lib/active_support/callbacks.rb:373:in `_run__795012590__call__callbacks'
activesupport (4.0.0) lib/active_support/callbacks.rb:80:in `run_callbacks'
actionpack (4.0.0) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/reloader.rb:64:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/remote_ip.rb:76:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'
activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'
railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'
rack (1.5.2) lib/rack/runtime.rb:17:in `call'
activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call'
rack (1.5.2) lib/rack/lock.rb:17:in `call'
actionpack (4.0.0) lib/action_dispatch/middleware/static.rb:64:in `call'
railties (4.0.0) lib/rails/engine.rb:511:in `call'
railties (4.0.0) lib/rails/application.rb:97:in `call'
rack (1.5.2) lib/rack/content_length.rb:14:in `call'
thin (1.6.1) lib/thin/connection.rb:82:in `block in pre_process'
thin (1.6.1) lib/thin/connection.rb:80:in `catch'
thin (1.6.1) lib/thin/connection.rb:80:in `pre_process'
thin (1.6.1) lib/thin/connection.rb:55:in `process'
thin (1.6.1) lib/thin/connection.rb:41:in `receive_data'
eventmachine (1.0.3) lib/eventmachine.rb:187:in `run_machine'
eventmachine (1.0.3) lib/eventmachine.rb:187:in `run'
thin (1.6.1) lib/thin/backends/base.rb:73:in `start'
thin (1.6.1) lib/thin/server.rb:162:in `start'
rack (1.5.2) lib/rack/handler/thin.rb:16:in `run'
rack (1.5.2) lib/rack/server.rb:264:in `start'
railties (4.0.0) lib/rails/commands/server.rb:84:in `start'
railties (4.0.0) lib/rails/commands.rb:78:in `block in <top (required)>'
railties (4.0.0) lib/rails/commands.rb:73:in `tap'
railties (4.0.0) lib/rails/commands.rb:73:in `<top (required)>'
bin/rails:4:in `require'
bin/rails:4:in `<main>'
就我而言我刚刚进行了回滚迁移，然后再次执行它，解决了此问题之后