## Flash

```ruby
# supports only notice and alert by default
# the rest has to go into flash hash
redirect_to :index, notice: "success"
redirect_to :new, notice: "errors"
redirect_to :new, flash: { success: "yeah" }
flash[:info] = "updated"

flash.now[:notice] = "wrong params" # sets the flash data in the current request
flash.keep # keeps the flash data for the next request
```

## Callbacks

```ruby
before_action  :do_authentication # calls the method
after_action   :do_compresssion
around_action  :do_something      # your method needs to call yield

skip_before_action
skip_after_action
skip_around_action

before_action :do_authentication, only: [:create, :delete]
before_action :do_authentication, except: [:create, :delete]
```

## default_url_options
- Sets the default URL params
- Will be overriden by params passed in

```ruby
class ApplicationController < ActionController::Base
  def default_url_options
    { locale: I18n.locale }
  end
end
```

## Set response

```ruby
respond_to :json # and works with respond_with Products.all

respond_to do |format|
  format.html { render :index }
  format.json { render xml: @products.to_json }
  format.js   { render 'partials' } # for AJAX calls with button_to remote: true
  format.xml  { render xml: @products.to_xml
```

## Filtering for authentication

```ruby
class ApplicationController < ActionController::Base

  before_action :abacus_authenticate, except: :login

  def login
    # do login
  end

  def abacus_authenticate
    render text: 'Unauthorized Access', status: '401' if session[:user_id].nil?
  end
end
```