ruby-on-rails ruby-on-rails-5 rails-generators

How to write a rails generator that would override the default scaffold javascript file?

Background:

Currently writing a gem

One of its features is that when rails generate my_gem_name:install is run, it (should) override the default javascript scaffold generated file (which is produced by rails generate scaffold some_model_name):

app/assets/javascripts/some_model_name.coffee

From:

# Place all the behaviors and hooks related to the matching controller here.
# All this logic will automatically be available in application.js.
# You can use CoffeeScript in this file: http://coffeescript.org/

To:

# Place all the behaviors and hooks related to the matching controller here.
# All this logic will automatically be available in application.js.
# You can use CoffeeScript in this file: http://coffeescript.org/

SomeJavascriptCode.doSomething({model: 'SomeModelName'})

Question:

How to write the said Rails generator (from above) that would override the default scaffold javascript file that is created by rails generate scaffold some_model_name.
Take note that the desired javascript file (as shown above), has dynamic contents; that is {model: 'SomeModelName'} should change & match correctly with the model name being generated.

Attempts:

I realised that there are two steps to solve this:
- simply just being able to override the scaffold-generated javascript file
- then, do something that would make the contents of said generated javascript file, to have "dynamic" contents.
1st step:
- Trying to write a generator that would copy my template file into Rails' AssetsGenerator template, eventually (hoping) to override it.
```
# lib/generators/my_gem_name/install_generator.rb
module MyGemName
  class InstallGenerator < Rails::Generators::Base
    source_root File.expand_path('../templates', __FILE__)

    class_option :javascript_engine, desc: 'JS engine to be used: [js, coffee].'

    def copy_js_scaffold_template
      copy_file "javascript.#{javascript_engine}", "lib/templates/coffee-rails/assets/javascript.#{javascript_engine}"
    end

    private

    def javascript_engine
      options[:javascript_engine]
    end
  end
end

# lib/generators/my_gem_name/templates/javascript.coffee
console.log('JUST TESTING!!!!!!!')
```
  - I temporarily used the path lib/templates/coffee-rails/assets/javascript.coffee just to test it out as the default javascript_engine is coffee. Probably that should change depending on --javascript_engine), but can't seem to make it work. I got this path from this LINK and then by referencing THIS:
    
    It seems that the pattern is flowing: lib/templates/gem_name/generator_name/template_file_name.rb
  - From this LINK, I also tried using the paths (but didnt work):
    - lib/templates/rails/assets/javascript.coffee
    - lib/templates/rails/assets/coffee/javascript.coffee
- 2nd Step: No attempts so far yet, as I'd like to make 1st Step above to work first.

All of my attempts above doesn't work: that is after both rails generate my_gem_name:install is ran, then running rails generate scaffold some_model_name still produces the original default javascript file, and not the expected console.log('JUST TESTING!!!!!!!') content (as I described above)

Solution

I finally solved it by the following. Hopefully, it would be helpful to anyone:

For Step 1 (Overriding the javascript file):

The problem was the override-path is not

lib/templates/gem_name/generator_name/template_file_name.rb

but

lib/templates/module_name/generator_name/template_file_name.rb

This I verified after looking at Coffe-Rails Generator Code and then trying out the following (which worked: the scaffold-generated javascript file now gets overriden after running rails generate my_gem_name:install then followed by the scaffold generator rails generate scaffold some_model_name)
```
# I temporarily hardcoded `coffee` as the `javascript_engine` to demonstrate, but `js` also works.
copy_file "javascript.coffee", "lib/templates/coffee/assets/javascript.coffee"
```

For Step 2 (Dynamic javascript file content):

After some trial-and-error, I noticed that you could actually insert <%= ... %> inside the javascript file, but then rename the template into a ruby file extension. The template seemingly gets rendered like how Rails views work when you insert <%= ... %> inside the file.

Complete Solution Looks Like:

lib/generators/my_gem_name/install_generator.rb

module MyGemName
  class InstallGenerator < Rails::Generators::Base
    source_root File.expand_path('../templates', __FILE__)

    class_option :javascript_engine, desc: 'JS engine to be used: [js, coffee].'

    def copy_js_scaffold_template
      copy_file "javascript.#{javascript_engine}.rb", "lib/templates/#{javascript_engine}/assets/javascript.#{javascript_engine}"
    end

    private

    def javascript_engine
      options[:javascript_engine]
    end
  end
end

lib/generators/my_gem_name/templates/javascript.coffee.rb

# Place all the behaviors and hooks related to the matching controller here.
# All this logic will automatically be available in application.js.
# You can use CoffeeScript in this file: http://coffeescript.org/
SomeJavascriptCode.doSomething({model: '<%= singular_table_name.camelcase %>'})

Then, on terminal:

rails generate my_gem_name:install
  Running via Spring preloader in process 42586
        create lib/templates/coffee/assets/javascript.coffee

rails generate scaffold user email first_name last_name
  Running via Spring preloader in process 43054
        invoke active_record
        create   db/migrate/20170721152013_create_users.rb
        create   app/models/user.rb
        ...
        invoke assets
        invoke   coffee
        create     app/assets/javascripts/users.coffee
        ...

cat app/assets/javascripts/users.coffee
  # Place all the behaviors and hooks related to the matching controller here.
  # All this logic will automatically be available in application.js.
  # You can use CoffeeScript in this file: http://coffeescript.org/
  SomeJavascriptCode.doSomething({model: 'User'})