Question

I am trying to update a rails model but I am facing some errors with the data handling even though the ajax request does go through.

The parameters being sent appears as shown below:

Parameters: {"{\"slot_allocation\":{\"timeslot_id\":\"3\",\"subject_id\":\"3\",\"slot_allocation_id\":\"1\",\"group_index\
":\"Group 2\",\"lesson_type\":\"Tutorial\"}}"=>nil, "id"=>"1"}
  SlotAllocation Load (0.2ms)  SELECT "slot_allocations".* FROM "slot_allocations" WHERE "slot_allocations"."id" = ? LIMIT 1
  [["id", "1"]]

Whereas a normal update does:

  Parameters: {"utf8"=>"✓", "authenticity_token"=>"yBib4ftNdB/r25uZuGnqEZI+r9dulVhyoce8nWBfcBQ=", "slot_allocation"=>{"slot_
allocation_id"=>"1", "lesson_type"=>"Lecture", "group_index"=>"Group 1", "timeslot_id"=>"1", "subject_id"=>"1"}, "commit"=>"
Update Slot allocation", "id"=>"1"}
  SlotAllocation Load (0.3ms)  SELECT "slot_allocations".* FROM "slot_allocations" WHERE "slot_allocations"."id" = ? LIMIT 1
  [["id", "1"]]

I am not sure where I have gone wrong being new to Rails and JSON.

I have tried out solutions posted by How do I parse JSON with Ruby on Rails?. But after changing my codes the requests does not get sent out. I have also tried changing the data being sent by following certain examples but it didn’t work out as well.

I would appreciate advice on what I could do to solve this error.

The following are the relevant codes:

My Ajax request:

var url = 'slot_allocations/'+alloc_id;

var dataToServer = {"slot_allocation":{"timeslot_id":timeslot, "subject_id":subject,"slot_allocation_id":alloc_id, "group_index":"Group 2", "lesson_type":"Tutorial"}}

  $.ajax({
    type: "PUT",
    url: url, 
    dataType: "json",
    data: JSON.stringify(dataToServer) 
    });

My controller update action:

  def update
    @slot_allocation = SlotAllocation.find(params[:id])

    respond_to do |format|
     if @slot_allocation.update_attributes(params[:slot_allocation])
        format.html { redirect_to @slot_allocation, notice: 'Slot allocation was successfully updated.' }
        format.json { head :ok}
      else
        format.html { render action: "edit" }
        format.json { render json: @slot_allocation.errors, status: :unprocessable_entity }
        format.js  { render :js => @slot_allocation.errors, :status => :unprocessable_entity }
      end
    end
  end

I would appreciate any advice on where I might have gone wrong. Thanks!

Answer 1

update_attributes expects a Hash. By converting the data you send to the server to JSON, params contains a JSON string instead. You should call the controller with standard POST data:

$.ajax({
  type: "PUT",
  url: url, 
  dataType: "json",
  data: dataToServer
});