Ruby on rails的新手，我刚收到此错误，无法弄清楚我哪里出错了。
如果它有助于消息模型遵循Michael Hartl的rails教程书中与micropost相同的设计。
错误读取
uninitialized constant Message::UserId
微量
activerecord (4.2.2) lib/active_record/inheritance.rb:158:in `compute_type'
activerecord (4.2.2) lib/active_record/reflection.rb:271:in `compute_class'
activerecord (4.2.2) lib/active_record/reflection.rb:267:in `klass'
activerecord (4.2.2) lib/active_record/associations/association.rb:214:in `raise_on_type_mismatch!'
activerecord (4.2.2) lib/active_record/associations/belongs_to_association.rb:12:in `replace'
activerecord (4.2.2) lib/active_record/associations/singular_association.rb:17:in `writer'
activerecord (4.2.2) lib/active_record/associations/builder/association.rb:123:in `user_id='
activerecord (4.2.2) lib/active_record/attribute_assignment.rb:54:in `public_send'
activerecord (4.2.2) lib/active_record/attribute_assignment.rb:54:in `_assign_attribute'
activerecord (4.2.2) lib/active_record/attribute_assignment.rb:41:in `block in assign_attributes'
activerecord (4.2.2) lib/active_record/attribute_assignment.rb:35:in `each'
activerecord (4.2.2) lib/active_record/attribute_assignment.rb:35:in `assign_attributes'
activerecord (4.2.2) lib/active_record/associations/association.rb:169:in `initialize_attributes'
activerecord (4.2.2) lib/active_record/associations/association.rb:248:in `block in build_record'
activerecord (4.2.2) lib/active_record/core.rb:283:in `initialize'
activerecord (4.2.2) lib/active_record/inheritance.rb:61:in `new'
activerecord (4.2.2) lib/active_record/inheritance.rb:61:in `new'
activerecord (4.2.2) lib/active_record/reflection.rb:131:in `build_association'
activerecord (4.2.2) lib/active_record/associations/association.rb:247:in `build_record'
activerecord (4.2.2) lib/active_record/associations/collection_association.rb:146:in `build'
activerecord (4.2.2) lib/active_record/associations/collection_proxy.rb:259:in `build'
actionpack (4.2.2) lib/action_controller/metal/implicit_render.rb:4:in `send_action'
actionpack (4.2.2) lib/abstract_controller/base.rb:198:in `process_action'
actionpack (4.2.2) lib/action_controller/metal/rendering.rb:10:in `process_action'
actionpack (4.2.2) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
activesupport (4.2.2) lib/active_support/callbacks.rb:117:in `call'
activesupport (4.2.2) lib/active_support/callbacks.rb:117:in `call'
activesupport (4.2.2) lib/active_support/callbacks.rb:555:in `block (2 levels) in compile'
activesupport (4.2.2) lib/active_support/callbacks.rb:505:in `call'
activesupport (4.2.2) lib/active_support/callbacks.rb:505:in `call'
activesupport (4.2.2) lib/active_support/callbacks.rb:92:in `_run_callbacks'
activesupport (4.2.2) lib/active_support/callbacks.rb:776:in `_run_process_action_callbacks'
activesupport (4.2.2) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (4.2.2) lib/abstract_controller/callbacks.rb:19:in `process_action'
actionpack (4.2.2) lib/action_controller/metal/rescue.rb:29:in `process_action'
actionpack (4.2.2) lib/action_controller/metal/instrumentation.rb:32:in `block in process_action'
activesupport (4.2.2) lib/active_support/notifications.rb:164:in `block in instrument'
activesupport (4.2.2) lib/active_support/notifications/instrumenter.rb:20:in `instrument'
activesupport (4.2.2) lib/active_support/notifications.rb:164:in `instrument'
actionpack (4.2.2) lib/action_controller/metal/instrumentation.rb:30:in `process_action'
actionpack (4.2.2) lib/action_controller/metal/params_wrapper.rb:250:in `process_action'
activerecord (4.2.2) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
actionpack (4.2.2) lib/abstract_controller/base.rb:137:in `process'
actionview (4.2.2) lib/action_view/rendering.rb:30:in `process'
actionpack (4.2.2) lib/action_controller/metal.rb:196:in `dispatch'
actionpack (4.2.2) lib/action_controller/metal/rack_delegation.rb:13:in `dispatch'
actionpack (4.2.2) lib/action_controller/metal.rb:237:in `block in action'
actionpack (4.2.2) lib/action_dispatch/routing/route_set.rb:74:in `call'
actionpack (4.2.2) lib/action_dispatch/routing/route_set.rb:74:in `dispatch'
actionpack (4.2.2) lib/action_dispatch/routing/route_set.rb:43:in `serve'
actionpack (4.2.2) lib/action_dispatch/journey/router.rb:43:in `block in serve'
actionpack (4.2.2) lib/action_dispatch/journey/router.rb:30:in `each'
actionpack (4.2.2) lib/action_dispatch/journey/router.rb:30:in `serve'
actionpack (4.2.2) lib/action_dispatch/routing/route_set.rb:819:in `call'
rack (1.6.4) lib/rack/etag.rb:24:in `call'
rack (1.6.4) lib/rack/conditionalget.rb:25:in `call'
rack (1.6.4) lib/rack/head.rb:13:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/params_parser.rb:27:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/flash.rb:260:in `call'
rack (1.6.4) lib/rack/session/abstract/id.rb:225:in `context'
rack (1.6.4) lib/rack/session/abstract/id.rb:220:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/cookies.rb:560:in `call'
activerecord (4.2.2) lib/active_record/query_cache.rb:36:in `call'
activerecord (4.2.2) lib/active_record/connection_adapters/abstract/connection_pool.rb:649:in `call'
activerecord (4.2.2) lib/active_record/migration.rb:378:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
activesupport (4.2.2) lib/active_support/callbacks.rb:88:in `call'
activesupport (4.2.2) lib/active_support/callbacks.rb:88:in `_run_callbacks'
activesupport (4.2.2) lib/active_support/callbacks.rb:776:in `_run_call_callbacks'
activesupport (4.2.2) lib/active_support/callbacks.rb:81:in `run_callbacks'
actionpack (4.2.2) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/reloader.rb:73:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/remote_ip.rb:78:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/debug_exceptions.rb:17:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'
railties (4.2.2) lib/rails/rack/logger.rb:38:in `call_app'
railties (4.2.2) lib/rails/rack/logger.rb:20:in `block in call'
activesupport (4.2.2) lib/active_support/tagged_logging.rb:68:in `block in tagged'
activesupport (4.2.2) lib/active_support/tagged_logging.rb:26:in `tagged'
activesupport (4.2.2) lib/active_support/tagged_logging.rb:68:in `tagged'
railties (4.2.2) lib/rails/rack/logger.rb:20:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/request_id.rb:21:in `call'
rack (1.6.4) lib/rack/methodoverride.rb:22:in `call'
rack (1.6.4) lib/rack/runtime.rb:18:in `call'
activesupport (4.2.2) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
rack (1.6.4) lib/rack/lock.rb:17:in `call'
actionpack (4.2.2) lib/action_dispatch/middleware/static.rb:113:in `call'
rack (1.6.4) lib/rack/sendfile.rb:113:in `call'
railties (4.2.2) lib/rails/engine.rb:518:in `call'
railties (4.2.2) lib/rails/application.rb:164:in `call'
rack (1.6.4) lib/rack/lock.rb:17:in `call'
rack (1.6.4) lib/rack/content_length.rb:15:in `call'
rack (1.6.4) lib/rack/handler/webrick.rb:88:in `service'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/webrick/httpserver.rb:138:in `service'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/webrick/httpserver.rb:94:in `run'
C:/RailsInstaller/Ruby2.0.0/lib/ruby/2.0.0/webrick/server.rb:295:in `block in start_thread'
答案 0 :(得分：3)
您似乎在调用未定义的关联模型user.messages
为了使其工作，您需要在两个模型中定义关联。
class User < ActiveRecord::Base
has_many :messages
end
class Messages < ActiveRecord::Base
belongs_to :user
end