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Rails - pass a parameter to controller from form select dropdown

I have 2 models: Team and Quest. When creating a new team, I have a drop-down of all the quests. When a quest is selected, I want to display information about the quest.
My understanding is that everything in the form is on the client side and AJAX is required to pass the selected quest to the server side. My code is based on this Stack Overflow answer.
Here is how I constructed my form:
app/views/teams_form.html.erb
<%= form_for(#team) do |f| %>
<fieldset>
<ol>
<li>
<%= f.label :name %>
<%= f.text_field :name %>
</li>
<li>
<%= f.label :quest_id %>
<%= f.select :quest_id,
options_from_collection_for_select(#quests, :id, :name),
{}, {remote: true, url: '/teams/new', method: 'get'} %>
</li>
<% if #x != nil && #x.id != nil %>
<li><%= #x.id %></li>
<% end %>
</ol>
<p>
<%= f.submit %>
</p>
</fieldset>
<% end %>
app/controllers/team_controller.rb
def new
#team = Team.new
#quests = Quest.all
respond_to do |format|
if params[:quest_id] != nil
#x = Quest.find(params[:quest_id])
end
format.html #new.html.erb
format.json
format.js
end
end
My goal was to pass the :quest_id parameter from the form to the #x variable and use that in the form.
This has produced nothing. I'm not getting the parameter in the controller and I'm not sure what I'm missing.

As per the description shared it seems like the you are unable to get the value of the selected item from the dropdown.
Below mentioned code is used for selecting value from dropdown also you can inspect the same using developer tools of the browser.
quest = $("#quest_id").val();
Note: Assuming the selector id is quest_id, change it according to your form.
Now, you can call the ajax using the below mentioned code.
$.ajax({
type: "GET",
url: "/teams/new",
data:{ quest_id: quest },
dataType: "json",
success:function(data){
# logic for using ajax result
}
Hope it helps!!

Finally got this working, wanted to post if anyone sees this and is having the same problem:
I went with a separate AJAX request since that was being suggested
app/views/teams_form.html.erb
<script>
$(document).ready(function() {
$('#team_quest_id').change(function() {
$.ajax({
url: "/teams/new",
data: {quest_id: $("#team_quest_id option:selected").val()},
dataType: "script",
method: "get",
success: function(r){}
});
});
});
</script>
I moved the location of the parameter assignment
app/controllers/team_controller.rb
def new
#team = Team.new
#quests = Quest.all
if params[:quest_id] != nil
#x = Quest.find(params[:quest_id])
end
respond_to do |format|
format.html #new.html.erb
format.json
format.js
end
end
And most importantly - I created a js file to render my form
app/views/new.js.erb
$('#new_team').html("<%= j (render 'form') %>");
This video was extremely helpful

The code in your question is almost correct, you forgot to nest the attributes in data.
<% # app/views/teams_form.html.erb %>
<%= f.select :quest_id,
options_from_collection_for_select(#quests, :id, :name),
{}, {remote: true, url: '/teams/new', method: 'get'} %>
<% # should be: %>
<%= f.select :quest_id,
options_from_collection_for_select(#quests, :id, :name),
{}, {data: {remote: true, url: '/teams/new', method: 'get'}} %>
<% # or even better, use the path helper instead of the hard coded path %>
<%= f.select :quest_id,
options_from_collection_for_select(#quests, :id, :name),
{}, {data: {remote: true, url: new_team_path, method: :get}} %>
Having set the attributes correctly, we still need to fix the form further. On page request the browser will request the form, but #x will never be set. Since ERB will not be send to the client we'll need to add a handle to find our quest container element back.
<% # app/views/teams_form.html.erb %>
<% if #x != nil && #x.id != nil %>
<li><%= #x.id %></li>
<% end %>
<% # should be something like %>
<li id="quest-info-container"></li>
Now in the controller split of the HTML request from the JS request.
# app/controllers/teams_controller.rb
def new
respond_to do |format|
format.html do
#team = Team.new
#quests = Quest.all
end
format.js do
#quest = Quest.find(params.dig(:team, :quest_id))
end
end
end
You could simplify the above by sending the select data-path to another url that handles the quest preview.
Now we need to render the preview in our container we need 2 files for this, first of how the resulting structure should look. Keep in mind that this will be rendered inside the container.
<% # app/views/teams/_quest_preview.html.erb %>
<% # Here comes what you want to display about the quest. You can give this %>
<% # file another name if you like. You have #quest to your disposal here. %>
<%= #quest.id %> <strong><%= #quest.name %></strong>
Now we only need a JavaScript file that loads the above structure into our created handle.
<% # app/views/teams/new.js.erb %>
handle = document.getElementById('quest-info-container');
handle.innerHTML = '<%= j render('quest_preview') %>';
The j is an alias for escape_javascript. If the partial is not in the same directory use <%= j render('other_dir/some_partial') %> instead.

select user and then dropdown of his challenges

A user has_many challenges.
When a user is selected...
<%= f.select :user_id, options_for_select(#challengers.collect { |challenger| [challenger.full_name] }) %>
... how can we show another dropdown with a list of his challenges?
<%= f.select :challenge_id, options_for_select(#challenger_challenges.collect { |challenged| [challenged.full_challenge]}) %>
In other words, how can we make "#challenger_challenges = the selected user's challenges"?
As it stand I get an error undefined method 'collect' for nil:NilClass since #challenger_challenges is nil.
OPTION 1
In challenges_controller I could do this:
#challengers = User.all
#challenger = User.find(params[:challenger_selected]) if (params[:challenger_selected]).present?
#challenger_challenges = #challenger.challenges
And then I would just need a way to refresh the page once a user is selected so that the user ID is passed in the params as :challenger_selected
OPTION 2
Achieve the aim of this question without the need of a page refresh. *Preferable
UPDATE
Based upon the comments below I realize I need to elaborate.
A user has_many challenges.
A user can create a duel.
In a duel there are two duelers.
The creator of the duel selects his own :challenge_id and then he selects the other dueler as well as one of his :challenge_id and then sets the #duel.consequence the dueler will have to do if he fails his challenge. The other dueler will get a duel request notification and then has the choice to accept or decline the conditions of the duel.
challenges.show.html.erb
<%= render 'duels/form' %>
duels/_form.html.erb
<%= simple_form_for(#duel) do |f| %>
<%= f.fields_for :duelers do |dueler| %>
<%= f.hidden_field :challenge_id, :value => #challenge.id %>
<%= #challenge.full_challenge %>
<% end %>
<%= f.fields_for :duelers do |dueler| %>
<%= render 'duels/dueler_fields', :f => dueler %>
<% end %>
<%= button_tag(type: 'submit', class: "btn", id: "challenge-create-save") do %>
Request Duel
<% end %>
<% end %>
duels/_dueler_fields.html.erb
<%= f.select :user_id, options_for_select(#challengers.collect { |challenger| [challenger.id] }) %>
# Trying to make this responsive to the user that is selected above
<%= render 'challenges/select', :f => f %>
<script>
$('#duel_duelers_attributes_1_user_id').change(function () {
var challenger_id = $(this).find(":selected").val();
var address = "<%= select_path %>".concat(challenger_id);
$.get(address, function(data) {
$("#duel_duelers_attributes_1_challenge_id").html(data);
});
});
</script>
routes
get 'challenges/select/:id' => 'challenges#select', as: 'select'
challenges/_select.html.erb
<%= f.select :challenge_id, options_for_select(#challenger_challenges.collect { |challenged| [challenged.full_challenge]}) %>
challenges_controller
def select
if (params[:challenger_id]).present?
#challenger = User.find(params[:challenger_id])
else
#challenger = User.find(1)
end
#challenger_challenges = #challenger.challenges
end

Credit for this should go to #Fallenhero - I am just explaining it in more detail.
You need to be able to identify the select tag.
<%= f.select ..., :html => {:id => :first} %>
You also need somewhere to put the second one.
<div id="second"></div>
Using jQuery:
$('#first').change(function () {
var challenger_id = $(this).find(":selected").val();
var address = "<%= [prints address to new select tag] %>".concat(challenger_id);
$.get(address, function(data) {
$("#second").html(data);
});
});
The address Ruby prints out should look something like challenges/select/ depending on how you want to design it. The / at the end is important.

jQuery .load()-function doesn't reload element (Rails)

In my Rails Project, I am trying to alter an instance variable via JS in a controller response (create.js.erb) and then reload an HTML-Element that makes use of the instance variable. But it doesn't work. Is it possible? This is just an example.
I also want to display the newly created object. But as I don't seem to understand the mechanism of exchanging information between rails and JS, I wanted to keep it simple here.
vocabs-controller.rb
def new
#user = current_user
#vocab = #user.vocabs.build
#vocabs = #user.vocabs.all
#count = #vocabs.count
.
.
end
def create
#user = current_user
#vocab = #user.vocabs.build(vocab_params)
#count = #user.vocabs.count
.
.
respond_to do |format|
format.html do
redirect_to new_user_vocab_path(#user)
flash[:success] = "Vocab created!"
end
format.js {render :layout=>false}
end
else
respond_to do |format|
format.html {render 'vocabs/new'}
format.js
end
end
new.html.erb (from here I make the call to the controllers create action)
<div class="panel-body">
<%= form_for(#vocab,
url: user_vocabs_path(#user),
method: :post, remote: true) do |f| %>
.
.
.
<%= f.submit "Add", class: "btn btn-large btn-primary" %>
<% end %>
<h4>
<%= #count %> Vocabs in your collection
</h4>
<%= link_to "(Show)", "#", id: "show_link" %>
<%= link_to "(Hide)", "#", id: "hide_link" %>
<ul class='vocabs <%= #vocabs_class %>'>
<% #vocabs.each do |vocab| %>
<%= render vocab %>
<% end %>
</ul>
<hr>
<%= link_to "Back", home_user_path(#user) %>
</div>
.
.
create.js.erb
<% #count+=1 %>
$('h4').load();
The server recognizes that I made a JS request and also renders create.js.erb with 200 OK. But the .load() function doesn't seem to reload the h4-Element with the new data.
When I was trying to .load() the div-element that contains the formular fields, these also weren't updated. The text input was still visible.
Further question: Where can I debug the code in JS Controller responses? I can't find them neither in Chrome's dev tools nor in Rails's server output.

If I follow you correctly, try
Add an id attribute to h4:
<h4 id="count-header">...</h4>
And in the .erb.js callback:
$('#count-header').text('<%= #count += 1 %> Vocabs in your collection');

Form_for doesn't work with JS/JQuery

I have problems getting a form to work when I use JavaScript with it.
Without the remote option set to true all works fine but as soon as I
set it, change the controller and create the needed JS files it produces an
POST .. 500 Internal Server Error
when clicking on the submit button.
Furthermore the reply-preview shows me a Rails Error Page saying
NoMethodError in Vocabs#create and undefined method > for nil:NilClass
in a related partial (which works fine before using JS)
The form (vocabs/_new_form.html.erb) looks like this:
<%= form_for #vocab, remote: true do |f| %>
<%= render 'fields', f: f %>
<%= f.submit "Add", class: "btn btn-large btn-primary" %>
<% end %>
The vocab_controller's create action like this:
def create
#user = current_user
#vocab = current_user.vocabs.build(vocab_params)
#vocabs = #user.vocabs.paginate(page: params[:page])
respond_to do |format|
format.html {
if #vocab.save
flash.now[:success] = "Vocab created!"
redirect_to root_url
else
flash.now[:error] = "Vocab not saved!"
render 'new'
end
}
format.js
end
end
The create.js.erb like this:
$('#new_vocab').remove();
Of course I want to do more than just to remove the form but as I didn't even manage to do that I wanted to keep it simple.
_fields.html.erb:
<%= render 'shared/error_messages', object: f.object %>
<div class="field">
<%= f.label :nl_word, #user.native_language %>
<%= f.text_field :nl_word %>
<%= f.label :fl_word, #user.foreign_language %>
<%= f.text_field :fl_word %>
<%= f.label :tag, "Your Tag" %>
<%= f.text_field :tag%>
<%= f.label :importance, "Importance" %>
<%= f.select(:importance, options_for_select(
StaticData::IMPORTANCE_SEED, :selected => f.object.importance)) %>
</div>
I hope I could explain myself good enough to get some help here. I tried for hours to find the solution to the problem myself and was looking for similar questions here without finding any and without getting anywhere.

With the help of a friend I found out that the main problem was that I didn't provide any validation for the vocab object i wanted to create in the form (_new_form.html.erb), when processing it with JS.
So I changed the vocab_controller.rb to
def create
#user = current_user
#vocab = current_user.vocabs.build(vocab_params)
#vocabs = #user.vocabs.paginate(page: params[:page])
respond_to do |format|
if #vocab.save
flash.now[:success] = "Vocab created!"
format.html do
redirect_to root_url
end
format.js
else
flash.now[:error] = "Vocab not saved!"
format.html do
render 'new'
end
format.js
end
end
end
That does the trick, and my form works with JS now.

Rails 3 javascript: How to render a partial with parameters

I'm still getting the hang of Rails. Here I'm using Rails 3 and the goal basically is to have an AJAX call triggered when I click the subscribe button the post_form partial is rendered beneath for the topic I have just subscribed to. The button then becomes an unsubscibe button and the post_form partial is removed. The toggling of the button alone works (i.e: by removing the second line in the two immediately following snippets), but the rendering of the *post_form* partial does not.
The problem is I can't seem to get the right syntax and/or passing of parameters in the two following partials. The topic object is just not passed and I get an invalid model_name for NilClass error when clicking on the subscribe or unsubscribe button. If I refresh the page manually, the partial is rendered or hidden the correct way, so it's really just the AJAX part that isn't working right.
views/subscription/create.js.erb
$("#subscription_form").html("<%= escape_javascript(render('users/unsubscribe')) %>");
$("#post_form").html("<%= escape_javascript(render('shared/post_form', :topic => #topic)) %>");
views/subscription/destroy.js.erb
$("#subscription_form").html("<%= escape_javascript(render('users/subscribe')) %>");
$("#post_form").html("<%= escape_javascript(render('shared/post_form', :topic => #topic)) %>");
views/users/_subscription_form.html.erb
<% unless current_user?(#user) %>
<div id="subscription_form">
<% if current_user.subscribed?(#topic) %>
<%= render 'users/unsubscribe', :topic => #topic %>
<% else %>
<%= render 'users/subscribe', :topic => #topic %>
<% end %>
</div>
<% end %>
controllers/subscriptions_controller.rb
class SubscriptionsController < ApplicationController
before_filter :signed_in_user
respond_to :html, :js
def create
#topic = Topic.find(params[:subscription][:topic_id])
current_user.subscribe!(#topic)
respond_with #topic
end
def destroy
#topic = Subscription.find(params[:id]).topic
current_user.unsubscribe!(#topic)
respond_with #topic
end
end
views/shared/_post_form.html.erb
<%= form_for(#post) do |f| %>
<div class="field">
<%= f.hidden_field :topic_id, :value => #topic.id %>
<%= f.text_area :content, placeholder: "Tell us about it ..." %>
</div>
<%= f.submit "Post", class: "btn btn-large btn-primary" %>
<% end %>
If it is of any help, the relationships are:
post -> belongs_to -> topic and topic -> has_many -> posts

Looks like you're using the variable "#post" in the "views/_post_form.html.erb" file.
<%= form_for(#post) do |f| %>
Since you aren't setting that variable anywhere in your actions you would get a null reference error.
You would need to do something like this:
def create
#post = Post.find(the_post_id)
#topic = Topic.find(params[:subscription][:topic_id])
current_user.subscribe!(#topic)
respond_with #topic
end
Also you are passing in the "topic" variable as a local but accessing it as an instance variable. You should change the your _post_form.html.erb file to look like this:
<%= form_for(#post) do |f| %>
<div class="field">
<%= f.hidden_field :topic_id, :value => topic.id %>
<%= f.text_area :content, placeholder: "Tell us about it ..." %>
</div>
<%= f.submit "Post", class: "btn btn-large btn-primary" %>
<% end %>
I don't have my ruby environment readily available so I can't verify that this will solve your problem but I think it should move you in the right direction.