ruby on rails - how to pass extra parameter to as_json from controller to model -

there 2 apis in controller. need image main_category , icon nav-category. how can pass xtra parameter controller , can differentiate in model request main_category , nav_category. please help.

def main_category     category = category.all     render :json => :include => {:success=> true,:data => category.as_json(@a,:only => [:name,:image_url])}    end    def nav_category     category = category.all     render :json => {:success=> true,:data => category.as_json(:only => [:name,:icon_url])}   end 

as_json in model :

def as_json(options = { })     if self.id == nil     category = self.category   elsif(@a=='main')     h = super(options)       h[:image_url]= "http://#{$request.try(:host_with_port)}#{self.image.url}"        h     else       h = super(options)       h[:image_url]= "http://#{$request.try(:host_with_port)}#{self.image.url}"       h[:icon_url]= "http://#{$request.try(:host_with_port)}#{self.icon.url}"       h     end end 

i think need passing custom option as_json method differentiate them.

controller:

def main_category   categories = category.all   render :json => {     :success=> true,     :data => categories.as_json(:only => [:name,:image_url], :category => "main")   } end  def nav_category   categories = category.all   render :json => {     :success=> true,     :data => categories.as_json(:only => [:name,:image_url], :category => "nav")   } end 

model :

def as_json(options = { })   h = super(options)   if (options[:category] == 'main') {     h[:image_url]= "http://#{$request.try(:host_with_port)}#{self.image.url}"   } elsif (options[:category] == 'nav') {     h[:image_url]= "http://#{$request.try(:host_with_port)}#{self.image.url}"     h[:icon_url]= "http://#{$request.try(:host_with_port)}#{self.icon.url}"   }    h end