What am I doing wrong with this AJAX request using a form_for in Rails 4?

Question

I'm trying to do a form submission through AJAX in Rails and I am not too sure what is wrong here. I got everything to work using "remote: true" but I want to gain a better understanding of how the AJAX works with jQuery. This is my javascript code:

$(document).ready(function(){
  $("#new_user_friendship").on("submit", function(event){
    event.preventDefault();
    var friendId = $("#user_friendship_friend_id").val();
    var _this = $(this);

    $.ajax({
      url: "/user_friendships",
      data: _this.serialize(),
      method: "POST",
      dataType: "json",
      success: function(data){
        console.log(data);
        friendButton.hide();
        $(".friend-request-form").html("<p>Friend request sent</p>");
      }
    });
  });
});

I am suspecting this line url: "/user_friendships/new?friend_id="+friendId containing the url is the culprit of my errors. I wrote this because a hidden field is being passed as a person's friend id but it throws a "404 error", I've also tried url: "/user_friendships" which doesn't return any errors but it also doesn't properly execute the Javascript as I expected.

This is the corresponding form_for that the AJAX request is sent to:

  <div class="friend-request-form">
      <%= form_for current_user.user_friendships.build(friend_id: @user), id: "new_user_friendship", method: :post do |f| %>

        <%= f.hidden_field :friend_id, value: @user.id  %>      
        <%= submit_tag "Send friend request", class: "button radius tiny", id: "friend-request-button" %>

      <% end %>
  </div>

What this form does is it sends a friend request to another user using a hidden field.

And in my user_friendships_controller.rb I have this code:

def create
    if params[:user_friendship] && params[:user_friendship].has_key?(:friend_id)
        @friend = User.find(params[:user_friendship][:friend_id])       
        @user_friendship = UserFriendship.request(current_user, @friend)

            respond_to do |format|
                if @user_friendship.new_record?
                    format.html do
                        flash[:error] = "There was a problem creating that friend request." 
                        redirect_to user_path(@friend)
                    end
                    format.json {render json: @user_friendship.to_json, status: :precondition_failed}

                else        
                    format.html do
                        flash[:success] = "Friend request sent"
                        redirect_to user_path(@friend)
                    end
                    format.json {render json: @user_friendship.to_json, status: :precondition_failed}
                end
            end 


    else
        flash[:error] = "Friend required"
        redirect_to root_path
    end
end

If anyone can provide any suggestions or feedback that'd be great!

UPDATE:

Now that I added in data: _this.serialize() and changed the url to: url: "/user_friendships" I'm now getting a 412 (Precondition Failed) error. Despite this error the data is actually being saved into the database. Does anyone know why I'm getting this 412 (Precondition Failed) error?

Answer 1

Add a data attribute to the post params instead of passing it in the url:

$.ajax({
  url: "/user_friendships",
  data: { user_friendship: { friend_id: friendId } }, // <<< Updated
  method: "POST",
  dataType: "json",
  success: function(data){
    console.log(data);
    friendButton.hide();
    $(".friend-request-form").html("<p>Friend request sent</p>");
  }
});

Update

The url should be /user_friendships , assuming that you're using RESTful actions. Have a look to this article about REST in Rails.

Also, when you do an AJAX request like this, your are not sending the rails authenticity tokens that are crated by the form helper . This may be the cause of your 412 (Precondition Failed) error.

See: Understanding the Rails Authenticity Token

Answer 2

There is something I do not understand, with the dataType json, you said that you had a precondition failed status right ? But you wrote

format.json {render json: @user_friendship.to_json, status: :precondition_failed}

So I don't think there is any problem, indeed, it seems to work fine, as you explicitly passed the status in your render command, try removing it and I think you will have a 200 (success) status instead. Of course, you can keep the previous post ajax request, or use this short version

$.post(
/user_friendships', 
{ user_friendship: { friend_id: friendId } }, 
function(){
    console.log(data);
    friendButton.hide();
    $(".friend-request-form").html("<p>Friend request sent</p>");
},
'json')