Rails: NameError: uninitialized constant

Ruby on-Rails Ruby on-Rails-4 Rails Console

Ruby on-Rails Problem Overview

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?

Ruby on-Rails Solutions

Solution 1 - Ruby on-Rails

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.

Solution 2 - Ruby on-Rails

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.

Solution 3 - Ruby on-Rails

I started having this issue after upgrading Rails 5.1 to 5.2
I got it solved with:

spring stop
spring binstub --all
spring start
rails s

Solution 4 - Ruby on-Rails

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

Solution 5 - Ruby on-Rails

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.

Solution 6 - Ruby on-Rails

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

Solution 7 - Ruby on-Rails

My problem was also solved by making sure that the filename was the same as the class name with the right conventions, that being for example class AdLikes has the filename ad_likes.rb

Solution 8 - Ruby on-Rails

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

Solution 9 - Ruby on-Rails

I had the same error. Turns out in my hasty scaffolding I left out the model.rb file.

Solution 10 - Ruby on-Rails

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.

Solution 11 - Ruby on-Rails

In my case, I named a column name type and tried to set its value as UNPREPARED. And I got an error message like this:

> Caused by: api_1 | NameError: uninitialized constant UNPREPARED

In rails, column type is reserved:

> ActiveRecord::SubclassNotFound: The single-table inheritance mechanism failed to locate the subclass: 'UNPREPARED'. This error is raised because the column 'type' is reserved for storing the class in case of inheritance. Pl ease rename this column if you didn't intend it to be used for storing the inheritance class or overwrite Food.inheritance_column to use another column for that information

Solution 12 - Ruby on-Rails

I had this same issue when working on a Rails 6 application in Ubuntu 20.04.

When I start the rails console using the command

rails console

and then run the command below to list all the available roles

Role.all

I get the error below:

Traceback (most recent call last):
        1: from (irb):2
NameError (uninitialized constant Role)

Here's how I fixed it:

The issue was that my Role model was namespaced with a module called Userbase. So instead of this:

Role.all

It should be this:

Userbase::Role.all

That's all

I hope this helps

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