How does my ajax call know where my json is in rails - ruby-on-rails

Question

I have a javascript file with some ajax in it as follows.
$.ajax({
type: "GET",
contentType: "application/json; charset=utf-8",
url: 'data',
dataType: 'json',
success: function (data) {
draw(data);
},
error: function (result) {
error();
}
});
I also have created a method in a controller which renders json.
class GraphController < ApplicationController
def index
end
def data
render :json => User.select('value').map(&:value)
end
end
So my question is, how does rails know where the json is coming from especially as I'm not returning a physical file from my controller. What happens if I also have a physical .json file in my folder structure? Is there a heirarchy of how a view will look for a json file (eg physical file>jbuilder file>controller action)?

Answer 1

Every Action must render something.
Either you render something explicitly or rails will look for a page with name similar to the action in inside respective controller's folder in views.
You may render an html.erb, .json, .haml etc from views( provided you specify respond to format)
If you are rendering someting explicitly (which is true in your case, as json) Rails wont bother to look into views folder.
Or otherwise you may just skip render :json statement and specify that object in .json file, with respond to :json.
Here in your scenario, you are rendering a json object, which will be accepted in the success: section of the AJAX function's data arguement.

Answer 2

in ajax call.. contentType: "application/json; charset=utf-8", defines what is the type of request you are querying with rails.What that says is, "if the client wants HTML in response to this action, just respond as we would have before, but if the client wants XML, return them the list of people in XML format." (Rails determines the desired response format from the HTTP Accept header submitted by the client.).
Take a look respond_to api how rails responds to different types of request -js/xml/html/json
so you can try this in your controller as well..edit the data action like this and try..any call to data such as js/html/xml/json will work and rails will understand what type of response it needs to send.
def data
format.html { redirect_to(user_list_url) }
format.js
format.xml { render :xml => #users.to_xml(:include => #accounts) }
format.json {render :json => User.select('value').map(&:value) }
end
to render any error from controller to view..can be done like this:-
if #user.present?
format.json {render :json => User.select('value').map(&:value) }
else
format.js { render :json => #user.errors.full_messages.join(' '),
:status => 400 }
end
use this in view in ajax.error function like this
.error(function(data) {
$("#show_error").html("An Error Occurred,Please try again.");
});
HOPE THIS HELPS