undefined method `simple_form_for' in RoR application

Question

I've been browsing stack overflow and I noticed that many people use simple_form to make their lives easier.

I wanted to give it a try, so I added the gem to my gem file (gem 'simple_form') and sent:

rails generate simple_form:install --bootstrap

After reading the installation message, I created a view with the sample code from the readme:

<%= simple_form_for @user do |f| %>
  <%= f.input :username %>
  <%= f.input :password %>
  <%= f.button :submit %>
<% end %>

Unfortunately, I get this error as soon as I try to load the page:

undefined method `simple_form_for' for #<#<Class:0x69dd688>:0x6903ac8>

What gives? How come it can't even recognize the method? I feel like I'm missing something really simply here. Could it be because i'm using bootstrap-sass? Do I need to include a helper in my user controller?

Abdication

did you restart server after install simple_form gem? – Valentinvalentina

doh! of course. I knew it was something silly like that. Thanks. – Abdication

Answer 1

Did you restart your server? Always keep in mind that after you install a gem or plugin. Always restart your server

Chiefly

Answer 2

Its all because you didn't restart your server after installing new libraries such as simple_form, devise etc.

Try stop your server and restart it. Your code is perfect!. I encountered this several times. The solution is just restarting the server!.

Adelric

Compared to the most upvoted and older answer, this does not provide any additional insight. – Sibbie

Answer 3

You must restart your server after installing simple_form gem.

Recession

Compared to the most upvoted and much older answer, this does not provide any additional insight. – Sibbie

Answer 4

For any absolute beginners. This error will occur if you forgot to install simple_form. To rectify, add this to your Gemfile

gem 'simple_form'

and bundle install

Thayer

Answer 5

To summarize all possibilities from above, hopefully this list is useful for other gems too.

1. Check if the simple_form gem is installed correctly

   Find the gem in Gemfile and Gemfile.lock. Another way is to run this command in your terminal: bundle list | grep simple_form

2. If the output is empty

   Possibly simple_form isn't installed in your project yet. Since the gem is an external gem, it isn't included in the Rails framework. Rails has its own form library (aka form_with and form_for).

   To add simple_form to your project, open the Gemfile and add gem 'simple_form', then run the command in your terminal bundle install.

3. If the output isn't empty

   Check if you have restart the server yet.

4. After restart the server, and you still not be able to access SimpleForm constant

   Check if the gem is set to require: false in Gemfile. If so, remove this part and run bundle install.

5. You can check if the gem is loaded from rails console by typing rails console or rails c in your terminal.

   After the console is loaded, type SimpleForm and hit Enter. In the case there is some errors complaining about the constant is undefined, refer to previous steps to fix.

Rosaline