Module: ActionController::ParamsWrapper

Wraps the parameters hash into a nested hash. This will allow clients to submit requests without having to specify any root elements.

This functionality is enabled in config/initializers/wrap_parameters.rb and can be customized.

You could also turn it on per controller by setting the format array to a non-empty array:

class UsersController < ApplicationController
  wrap_parameters format: [:json, :xml, :url_encoded_form, :multipart_form]
end

If you enable ParamsWrapper for :json format, instead of having to send JSON parameters like this:

{"user": {"name": "Konata"}}

You can send parameters like this:

{"name": "Konata"}

And it will be wrapped into a nested hash with the key name matching the controller’s name. For example, if you’re posting to UsersController, your new params hash will look like this:

{"name" => "Konata", "user" => {"name" => "Konata"}}

You can also specify the key in which the parameters should be wrapped to, and also the list of attributes it should wrap by using either :include or :exclude options like this:

class UsersController < ApplicationController
  wrap_parameters :person, include: [:username, :password]
end

On Active Record models with no :include or :exclude option set, it will only wrap the parameters returned by the class method attribute_names.

If you’re going to pass the parameters to an ::ActiveModel object (such as User.new(params[:user])), you might consider passing the model class to the method instead. The ParamsWrapper will actually try to determine the list of attribute names from the model and only wrap those attributes:

class UsersController < ApplicationController
  wrap_parameters Person
end

You still could pass :include and :exclude to set the list of attributes you want to wrap.

By default, if you don’t specify the key in which the parameters would be wrapped to, ParamsWrapper will actually try to determine if there’s a model related to it or not. This controller, for example:

class Admin::UsersController < ApplicationController
end

will try to check if Admin::User or User model exists, and use it to determine the wrapper key respectively. If both models don’t exist, it will then fallback to use user as the key.