rails 4, change default form builder globally - ruby-on-rails

Question

I have sub-classed the default form builder to add some additional methods. Sample code is below.
module ApplicationHelper
class AppFormBuilder < ActionView::Helpers::FormBuilder
def coordinates_field(method, options = {})
options[:readonly] = 'true'
....
#template.text_field(#object_name, method, objectify_options(options))
end
end
end
This works well, but to use it I have to change the view code for every form that uses the coordinates_field method, i.e.,
<%= form_for #object, :builder => ApplicationHelper::AppFormBuilder do |f| %>
...
<% end %>
It sounds like it is theoretically possible to change the default form builder globally (config.action_view.default_form_builder), but I can't seem to get this to work. This is what I have tried in /config/application.rb:
module Web
class Application < Rails::Application
...
config.action_view.default_form_builder = "ApplicationHelper::AppFormBuilder"
end
end
Which results in error undefined method 'new' for "ApplicationHelper::AppFormBuilder":String when I hit a view that has a form.
If I instead try this
config.action_view.default_form_builder = ApplicationHelper::AppFormBuilder
I get the error *config.action_view.default_form_builder = ApplicationHelper::AppFormBuilder* when the application starts.
Can anyone provide guidance on how to get this to work?

Answer 1

As mentioned in the official docs, in Rails 5 the correct way is to specify it in a controller. To make it application wide, just set in your ApplicationController:
class ApplicationController < ActionController::Base
default_form_builder AppFormBuilder
end
This makes much more sense. FormHelpers are part of the view layer and not the application config.

Answer 2

ApplicationHelper::AppFormBuilder is not required yet at the time application.rb loads. You can try to put this in a separate initializer file (create one in config\initializers):
module Web
class Application
ActionView::Base.default_form_builder = AppFormBuilder
end
end

Answer 3

I like Max's answer, but (rails n00b here so YMMV) I believe this is equivalent and cleaner, directly in config/application.rb:
config.after_initialize do
ActionView::Base.default_form_builder = MyCustomHelper::MyCustomFormBuilder
end
obviously you replace the names MyCustomHelper and MyCustomFormBuilder.
took me about 48hrs to figure this out, thanks to all that well-structured rails documentation.

Answer 4

You should be able to set this from an initializer as you would for other config options. Create a default_form_builder.rb file under config/initializers/. The syntax should simpler than in #Max's answer.
Rails.application.config.action_view.default_form_builder = AppFormBuilder
I suggest you do not include this in a helper. Add it as separate class inside the /lib directory. You may or may not need to prefix the with the module it's contained within.
Finally, you can set this globally from config/application.rb, but you would have to pass it as a string since the class may not be loaded when rails starts up.
config.action_view.default_form_builder = 'AppFormBuilder'

Answer 5

Rails 5+ 👌
class ApplicationController < ActionController::Base
default_form_builder AppFormBuilder
end
Rails 4 🏖
class ApplicationController < ActionController::Base
ActionView::Base.default_form_builder = AppFormBuilder
end
... or if you prefer an initializer, I'd recommend setting it as a string instead, that way you will not have to restart Rails every time you change something in your form builder.. 😴 (since the class may not be loaded when rails starts up. https://stackoverflow.com/a/27992240/2037928)
module Web
class Application
ActionView::Base.default_form_builder = "AppFormBuilder"
end
end