Rendering dynamic scss-files with ajax, rails - ruby-on-rails

Question

As the title suggests, my main objective is to render a dynamic scss(.erb) file after an ajax call.
assets/javascripts/header.js
// onChange of a checkbox, a database boolean field should be toggled via AJAX
$( document ).ready(function() {
$('input[class=collection_cb]').change(function() {
// get the id of the item
var collection_id = $(this).parent().attr("data-collection-id");
// show a loading animation
$("#coll-loading").removeClass("vhidden");
// AJAX call
$.ajax({
type : 'PUT',
url : "/collections/" + collection_id + "/toggle",
success : function() {
// removal of loading animation, a bit delayed, as it would be too fast otherwise
setTimeout(function() {
$("#coll_loading").addClass("vhidden");
}, 300);
},
});
});
});
controller/collections_controller.rb
def toggle
# safety measure to check if the user changes his collection
if current_user.id == Collection.find(params[:id]).user_id
collection = Collection.find(params[:id])
# toggle the collection
collection.toggle! :auto_add_item
else
# redirect the user to error page, alert page
end
render :nothing => true
end
All worked very smooth when I solely toggled the database object.
Now I wanted to add some extra spices and change the CSS of my 50+ li's accordingly to the currently selected collections of the user.
My desired CSS looks like this, it checks li elements if they belong to the collections and give them a border color if so.
ul#list > li[data-collections~='8'][data-collections~='2']
{
border-color: #ff2900;
}
I added this to my controller to generate the []-conditions:
def toggle
# .
# .
# toggle function
# return the currently selected collection ids in the [data-collections]-format
#active_collections = ""
c_ids = current_user.collections.where(:auto_add_item => true).pluck('collections.id')
if c_ids.size != 0
c_ids.each { |id| #active_collections += "[data-collections~='#{id}']" }
end
# this is what gets retrieved
# #active_collections => [data-collections~='8'][data-collections~='2']
end
now I need a way to put those brackets in a scss file that gets generated dynamically.
I tried adding:
respond_to do |format|
format.css
end
to my controller, having the file views/collections/toggle.css.erb
ul#list<%= raw active_collections %> > li<%= raw active_collections %> {
border-color: #ff2900;
}
It didn't work, another way was rendering the css file from my controller, and then passing it to a view as described by Manuel Meurer
Did I mess up with the file names? Like using css instead of scss? Do you have any ideas how I should proceed?
Thanks for your help!
Why dynamic CSS? - reasoning
I know that this should normally happen by adding classes via JavaScript. My reasoning to why I need a dynamic css is that when the user decides to change the selected collections, he does this very concentrated. Something like 4 calls in 3 seconds, then a 5 minutes pause, then 5 calls in 4 seconds. The JavaScript would simply take too long to loop through the 50+ li's after every call.
UPDATE
As it turns out, JavaScript was very fast at handling my "long" list... Thanks y'all for pointing out the errors in my thinking!

Answer 1

In my opinion, the problem you've got isn't to do with CSS; it's to do with how your system works
CSS is loaded static (from the http request), which means when the page is rendered, it will not update if you change the CSS files on the server
JS is client side and is designed to interact with rendered HTML elements (through the DOM). This means that JS by its nature is dynamic, and is why we can use it with technologies like Ajax to change parts of the page
Here's where I think your problem comes in...
Your JS call is not reloading the page, which means the CSS stays static. There is currently no way to reload the CSS and have them render without refreshing (sending an HTTP request). This means that any updating you do with JS will have to include per-loaded CSS
As per the comments to your OP, you should really look at updating the classes of your list elements. If you use something like this it should work instantaneously:
$('li').addClass('new');
Hope this helps?

Answer 2

If I understood your feature correctly, actually all you need can be realized by JavaScript simply, no need for any hack.
Let me organize your feature at first
Given an user visiting the page
When he checks a checkbox
He will see a loading sign which implies this is an interaction with server
When the loading sign stopped
He will see the row(or 'li") he checked has a border which implies his action has been accepted by server
Then comes the solution. For readability I will simplify your loading sign code into named functions instead of real code.
$(document).ready(function() {
$('input[class=collection_cb]').change(function() {
// Use a variable to store parent of current scope for using later
var $parent = $(this).parent();
// get the id of the item
var collection_id = $parent.attr("data-collection-id");
show_loading_sign();
// AJAX call
$.ajax({
type : 'PUT',
url : "/collections/" + collection_id + "/toggle",
success : function() {
// This is the effect you need.
$parent.addClass('green_color_border');
},
error: function() {
$parent.addClass('red_color_border');
},
complete: function() {
close_loading_sign(); /*Close the sign no matter success or error*/
}
});
});
});
Let me know if my understanding of feature is correct and if this could solve the problem.

Answer 3

What if, when the user toggles a collection selection, you use jquery change one class on the ul and then define static styles based on that?
For example, your original markup might be:
ul#list.no_selection
li.collection8.collection2
li.collection1
And your css would have, statically:
ul.collection1 li.collection1,
ul.collection2 li.collection2,
...
ul.collection8 li.collection8 {
border-color: #ff2900;
}
So by default, there wouldn't be a border. But if the user selects collection 8, your jquery would do:
$('ul#list').addClass('collection8')
and voila, border around the li that's in collection8-- without looping over all the lis in javascript and without loading a stylesheet dynamically.
What do you think, would this work in your case?