Using ajax to check something about variable in Rails - php

Question

I am new to Ruby on Rails, and I would like to know a Rails equivalent for something I am used to do using PHP.
When checking if a user input meets certain criteria, I usually make some Ajax calls using javascript to a php page that processes the data and echo a json data. I then use the json data to construct appropriate behaviors.
For instance, let's assume a user submitted a postcode and I want to run some checks on the postcode on server side. I would do something like this in js:
// This is what the user submitted
var postcode = $("#postcode").val();
// Here, I post it to a PHP file
// PHP file examines the data and returns result
// (in this case, if the postcode is covered or not)
$.post("scripts/postcode_handling.php", {postcode: postcode}, function(data) {
var result = jQuery.parseJSON(data);
// Check the coverage
if (result.coverage == true) {
// Do Something
} else {
// Do something
}
And on the php file I will do something like:
...
$result = array('coverage' => false , 'message' => "Your postcode is not covered")
echo json_encode($result);
....
I tried to do something similar in Rails by replacing the php file with an action under a controller, but I could not figure it out. Is this a common practice in Rails, and how can I do something like this?

Answer 1

Let's use your post code example. Let's say you wanted to do an address lookup based on post code.
Create a route
Create a controller and an action to handle the request
Create the Javascript logic to handle sending the request and DOM manipulation
Open a config/routes.rb and add a route:
resources :address_lookups, only: :new
Create a controller to handle the route:
rails g controller AddressLookups
The above command creates a new controller called address_lookups_controller.rb inside app/controllers.
Now add the necessary logic inside the controller to handle the address lookup:
class AddressLookupsController < ApplicationController
def new
# This action will expect a params[:post_code] variable
# that you will pass with your ajax request
post_code = params[:post_code]
address = FindSomeAddress.lookup(post_code)
render json: address
end
end
Now create a JavaScript handler to send the request and handle the return. If you generated the controller there should already be a file called address_lookups.js.coffee inside app/assets/javascripts. Here's some pseudo code.
jQuery ->
$('#post_code').on 'blur', ->
field = $(this)
post_code = field.val()
if post_code.length is 8
xhr = $.ajax
url: "/address_lookups/new"
data:
post_code: post_code
success: (data) ->
# do something with data
dataType: "json"