如何为控制器中的部分视图定义功能以在所有视图中工作？ Ruby on Rails

Question

For example, I'm placing the partial <%= render "layouts/location" %> in views all over the site. I need a controller for the layout (I tried layouts_controller.rb ) so I could do

def _location
    @city = request.location.city
    @state = request.location.state
  end

The partial contains the code <%= @city %>, <%= @state %>

This is all effectively, supposed to display the city and state of the visitor on whatever page the partial is rendered on.

When I do this however, and push to heroku and migrate the database, I'm served the error: An error occurred in the application and your page could not be served. Please try again in a few moments.

If you are the application owner, check your logs for details.

So the question is, how do I define a function for a partial?

Answer 1

You could do this in a before filter in your application controller like so:

...
before_filter :location

def location
    @city = request.location.city
    @state = request.location.state
end

The name of the method needs to match the symbol in the before_filter call, but other than that, you can call the method whatever you want. The method must be in the ApplicationController class though.

Clarification: This will get called before every request in your application and set these two instance variables for you, so in every view, you will always and automatically have access to @city and @state.

Answer 2

I feel like you can make a few improvements from the other solutions.

In ApplicationController

class ApplicationController < ActionController::Base
    before_filter :set_location, only: [:index, :show, :edit]

    def set_location
      @city = request.location.city
      @state = request.location.state
    end
end

It's likely that you don't need those variables for the create, update and destroy actions, so using only: [...] seems like a good idea. You can add other custom methods in there. The main problem with that will be when your create action will fail, and you'll want to render the "edit" page. If you don't need those variables on the edit page, then everything's fine. Otherwise, you'll need to call set_location yourself:

def create
    @lala = Lala.new(...)
    @lala.save
    set_location if @lala.errors.any?
    respond_with @lala
end

Also, in the 30% of pages that don't need those variables, you can use skip_before_filter :

 class BlogsController < ApplicationController
    #assume you dont need those variables in your blog

    skip_before_filter :set_location # you can also use only: [:index, ...] here
 end

Answer 3

You should take a look at cells . It is an awesome, but rather unknown gem that allows you to structure your application in "cells". It might be just what you need.