如何使用Ruby on Rails将MySQL纬度/经度数据转换为JSON

Question

Thanks in advance for any help you can provide on this question: How can I use Ruby on Rails to create a JSON object from the "latitude" and "longitude" data in my MySQL table, "Locations"?

My ultimate goal is to create a Google Map with multiple markers pulled from a MySQL database. I know that I can do this through PHP and the Google tutorial ( https://developers.google.com/maps/articles/phpsqlsearch_v3 ), but I'm not strong in PHP and am looking for a shorter way to do it through Rails.

I have tried this other tutorial ( http://mokisystemsblog.blogspot.com/2013/04/add-markers-to-google-map-with-ruby-on.html ), and here is my code for my controller:

    class MapallController < ApplicationController
      # GET /mapall
      # GET /mapall.xml
      # GET /mapall.js

      def index
        respond_to do |format|
          format.html do
            @locations = Location.find(:all)
          end
          format.xml  { render :xml => @locations }
          format.js do
            ne = params[:ne].split(',').collect{|e|e.to_f}  
            sw = params[:sw].split(',').collect{|e|e.to_f}
            @locations = Location.find(:all, :limit => 100, :bounds => [sw, ne])
            render :json => @locations.to_json
          end
        end
      end
    end

However, when I visit www.example.com/mapall.js, I get an error code. I expect that this link would give me the complete set of results from my database.

Again, I appreciate your advice and patience as I learn this process!

EDIT 1 - ERROR CODE

Below is the log for what happens when I visit example.com/mapall, example.com/mapall.js, and example.com/mapall.xml. When I visit example.com/mapall, I expect a Google Map that renders all of my locations from the MySQL database. Barring that, I expected to see the lat / long data when I visited mapall.js. From the log below, I'm guessing the reason that I'm getting a 404 is that there is no route to mapall.js in my routes file. Is the solution to create a route to the routes file, and if so, how should that read?

Thanks again for your help!

    Processing MapallController#index (for IP at DATE TIME) [GET]
    Rendering template within layouts/mapall
    Rendering mapall/index
    Completed in 779ms (View: 7, DB: 100) | 200 OK [http://example.com/mapall]

    Processing ApplicationController#index (for IP at DATE TIME) [GET]

    ActionController::RoutingError (No route matches "/mapall.js" with {:method=>:get}):
    /phusion_passenger ERROR INFO
    Rendering /home/example/web/current/public/404.html (404 Not Found)

    Processing ApplicationController#index (for IP at DATE TIME) [GET]

    ActionController::RoutingError (No route matches "/mapall.xml" with {:method=>:get}):
    /phusion_passenger ERROR INFO
    Rendering /home/example/web/current/public/404.html (404 Not Found)

EDIT 2 - New Controller

Thanks to @kyllo's feedback, I've been able to update the controller so that I can get ALL of my location data to appear at http://example.com/mapall.js . Only one step left: getting just the nickname, latitude, and longitude fields to appear. The below shows ALL of the data. How should I change this to show only the nickname, latitude, and longitudinal fields?

    class MapallController < ApplicationController
    # GET /mapall
    # GET /mapall.xml
    # GET /mapall.js

    def index
    respond_to do |format|
@masterlocation = Masterlocation.find(:all)
    format.html do
    end
    format.xml  { render :xml => @masterlocation }
    format.js do
    @masterlocation = Masterlocation.find(:all)
    render :json => @masterlocation.to_json
    end
    end
    end
    end

Answer 1

I see a few problems here.

Yes, you are getting a "no route matches" error so you need a route in routes.rb similar to this, so that you can access :format as a parameter to respond to:

match 'mapall.:format'

Then in your controller, you have the following:

def index
    respond_to do |format|
      format.html do
        @locations = Location.find(:all)
      end
      format.xml  { render :xml => @locations }
      format.js do
        ne = params[:ne].split(',').collect{|e|e.to_f}  
        sw = params[:sw].split(',').collect{|e|e.to_f}
        @locations = Location.find(:all, :limit => 100, :bounds => [sw, ne])
        render :json => @locations.to_json
      end
    end
  end

Your @locations = Location.find(:all) needs to be outside of the format.html do block, otherwise @locations is undefined inside of your format.xml block and you will get an error.

format.js do will allow your user to access the JSON API by visiting http:/www.example.com/mapall.js . If you use format.json do then they can access it at http:/www.example.com/mapall.json . The choice is yours.

Hope that helps to put you on the right track!