Rails 第一次将属性分配给我的模型时抛出错误
Rails is throwing an error the first time an attribute is assigned to my model
我有一个 rails 模型可以跟踪应用程序中的其他模型。 （不寻常，但对于这个项目是必要的）。
当我尝试分配属性 model_name 时，出现一次错误，但之后不会再发生。
AppModel
model_name created_at updated_at
----------------------------------------
User
Question
Post
Answer
在控制台中，我收到一个奇怪的错误：
> model = AppModel.new
> model.model_name = "User" # First time causes the error.
> model.model_name = "User" # Second time it works.
错误:
ActiveRecord::DangerousAttributeError: record_changed? is defined by Active Record
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:104:in `instance_method_already_implemented?'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:288:in `block in define_attribute_method'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:285:in `each'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:285:in `define_attribute_method'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:252:in `block in define_attribute_methods'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:252:in `each'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:252:in `define_attribute_methods'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:75:in `block in define_attribute_methods'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/mutex_m.rb:73:in `synchronize'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/mutex_m.rb:73:in `mu_synchronize'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:72:in `define_attribute_methods'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:196:in `method_missing'
from (irb):3
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/console.rb:90:in `start'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/console.rb:9:in `start'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/commands_tasks.rb:69:in `console'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:247:in `require'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:247:in `block in require'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:232:in `load_dependency'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:247:in `require'
from /Users/donaldpinkus/Projects/hooker/bin/rails:8:in `<top (required)>'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:241:in `load'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:241:in `block in load'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:232:in `load_dependency'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:241:in `load'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from -e:1:in `<main>'2.1.5 :004 > e.model_name = "User"
=> "User"
"model_name" 不是模型的保留字，所以这里发生了什么？
发生这种情况是因为在 ActiveRecord 模型中已经有一个方法，它被准确地称为 model_name，returns（显然）这个模型的名称（除其他外）。
- From:
.../ruby-2.1.5/gems/activemodel-4.2.0/lib/active_model/naming.rb
@ line 222:
- Owner: ActiveModel::Naming
- Visibility: public
- Signature: model_name()
- Number of lines: 12
Returns an ActiveModel::Name object for module. It can be used to
retrieve all kinds of naming-related information (See
ActiveModel::Name for more information).
当 ActiveRecord 从 table 中获取对象时，它还会创建名称与 table 中的列名称相对应的方法。发生的事情是它获取一个对象，在给定对象上看到一个列 model_name，尝试定义一个方法 model_name 并突然发现它已经存在。
注意事项：避免不必要的长属性名称。如果你在模型中定义一个名称，它可以只是 name，它的范围是 "model" class 无论如何，显然它是模型的名称。
但是，错误报告代码可能包含需要追踪的错误。
我有一个 rails 模型可以跟踪应用程序中的其他模型。 （不寻常，但对于这个项目是必要的）。
当我尝试分配属性 model_name 时，出现一次错误，但之后不会再发生。
AppModel
model_name created_at updated_at
----------------------------------------
User
Question
Post
Answer
在控制台中，我收到一个奇怪的错误：
> model = AppModel.new
> model.model_name = "User" # First time causes the error.
> model.model_name = "User" # Second time it works.
错误:
ActiveRecord::DangerousAttributeError: record_changed? is defined by Active Record
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:104:in `instance_method_already_implemented?'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:288:in `block in define_attribute_method'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:285:in `each'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:285:in `define_attribute_method'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:252:in `block in define_attribute_methods'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:252:in `each'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activemodel-4.1.4/lib/active_model/attribute_methods.rb:252:in `define_attribute_methods'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:75:in `block in define_attribute_methods'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/mutex_m.rb:73:in `synchronize'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/2.1.0/mutex_m.rb:73:in `mu_synchronize'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:72:in `define_attribute_methods'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activerecord-4.1.4/lib/active_record/attribute_methods.rb:196:in `method_missing'
from (irb):3
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/console.rb:90:in `start'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/console.rb:9:in `start'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/commands_tasks.rb:69:in `console'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/railties-4.1.4/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:247:in `require'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:247:in `block in require'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:232:in `load_dependency'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:247:in `require'
from /Users/donaldpinkus/Projects/hooker/bin/rails:8:in `<top (required)>'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:241:in `load'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:241:in `block in load'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:232:in `load_dependency'
from /Users/donaldpinkus/.rvm/gems/ruby-2.1.5/gems/activesupport-4.1.4/lib/active_support/dependencies.rb:241:in `load'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from /Users/donaldpinkus/.rvm/rubies/ruby-2.1.5/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:54:in `require'
from -e:1:in `<main>'2.1.5 :004 > e.model_name = "User"
=> "User"
"model_name" 不是模型的保留字，所以这里发生了什么？
发生这种情况是因为在 ActiveRecord 模型中已经有一个方法，它被准确地称为 model_name，returns（显然）这个模型的名称（除其他外）。
- From: .../ruby-2.1.5/gems/activemodel-4.2.0/lib/active_model/naming.rb @ line 222:
- Owner: ActiveModel::Naming
- Visibility: public
- Signature: model_name()
- Number of lines: 12
Returns an ActiveModel::Name object for module. It can be used to retrieve all kinds of naming-related information (See ActiveModel::Name for more information).
当 ActiveRecord 从 table 中获取对象时，它还会创建名称与 table 中的列名称相对应的方法。发生的事情是它获取一个对象，在给定对象上看到一个列 model_name，尝试定义一个方法 model_name 并突然发现它已经存在。
注意事项：避免不必要的长属性名称。如果你在模型中定义一个名称，它可以只是 name，它的范围是 "model" class 无论如何，显然它是模型的名称。
但是，错误报告代码可能包含需要追踪的错误。