问题
I have a simple model called PhoneNumber:
class PhoneNumber < ActiveRecord::Base
validates :pnumber, presence: true, on: :create #=> { :message => " cannot be blank" }
validates :pnumber, numericality: true, on: :create
end
I go to the root folder of the application (the one containing the app sub-folder) and start the console:
rails console --sandbox
When I try to create an empty PhoneNumber (I want to get an error message as the validation shall fail) I am getting the following error message:
2.0.0-p451 :001 > PhoneNumber.new
NameError: uninitialized constant PhoneNumber
from (irb):1
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/commands/console.rb:90:in `start'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/commands/console.rb:9:in `start'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:69:in `console'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/commands/commands_tasks.rb:40:in `run_command!'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/commands.rb:17:in `<top (required)>'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/app_rails_loader.rb:43:in `require'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/app_rails_loader.rb:43:in `block in exec_app_rails'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/app_rails_loader.rb:32:in `loop'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/app_rails_loader.rb:32:in `exec_app_rails'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/lib/rails/cli.rb:5:in `<top (required)>'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/bin/rails:9:in `require'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/gems/railties-4.1.5/bin/rails:9:in `<top (required)>'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/bin/rails:23:in `load'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/bin/rails:23:in `<main>'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/bin/ruby_executable_hooks:15:in `eval'
from /Users/nnikolo/.rvm/gems/ruby-2.0.0-p451@railstutorial_rails_4_0/bin/2.2.2.02.02.02.0.2.2.02.222222.2.02.02.0.2.2.022222222222222
It seems the console is not aware of the model. In plain ruby you need to 'require' the file containing the class but I thought that the rails console shall automatically load all models. What is going on here?
回答1:
Some things to try:
Restart the rails console; changes to your models will only get picked up by a rails console that is already open if you do
> reload!(although I have found this to be unpredictable), or by restarting the console.Is your model file called "phone_number.rb" and is it in "/app/models"?
You should double-check the "--sandbox" option on your rails console command. AFAIK, this prevents changes. Try it without the switch.
回答2:
I was getting the error:
NameError: uninitialized constant
Then I noticed that I had accidentally created a plural model so I went back and renamed the model file to singular and also changed the class name in the model file to singular and that solved it.
回答3:
I started having this issue after upgrading from Rails 5.1 to 5.2
It got solved with:
spring stop
spring binstub --all
spring start
rails s
回答4:
I ran into this also with a file directly in the models directory, and it turns out that I wasn't properly loading up the code on startup. I was able to fix the issue by setting config.eager_load = true in my development.rb file. This made the class available to me in the console
回答5:
Similar with @Michael-Neal.
I had named the controller as singular. app/controllers/product_controller.rb
When I renamed it as plural, error solved. app/controllers/products_controller.rb
回答6:
If none of the above work, I also have a different approach, as it happened to me in a real scenario.
More specifically using auto-generated Ruby files from Thrift.
In my situation, I had a Module with several classes, so the order is important in this case:
Class A makes use of Class B in the same module. However, Class B was declared after Class A.
Simply making Class B to be declared before Class A solved the issue to me.
回答7:
I had this problem because I changed the name of the class in a model, and it did not match the name of the file.
"Model class names use CamelCase. These are singular, and will map automatically to the plural database table name.
Model files go in app/models/#{singular_model_name}.rb."
https://gist.github.com/iangreenleaf/b206d09c587e8fc6399e#model
回答8:
I had the same error. Turns out in my hasty scaffolding I left out the model.rb file.
回答9:
I had a similar error, but it was because I had created a has_one relationship and subsequently deleted the model that it had_one of. I just forgot to delete the has_one relationship from the remaining model.
来源：https://stackoverflow.com/questions/26393445/nameerror-uninitialized-constant-rails