Ruby on Rails createmethod doesn't work

Question

I got a model day and a model task . day has many tasks . I'm using a nested_form for this. The user enters a time and two variables, which a caculated to an index . The first task, with the highest index has a starttime = 8am.
Now I want to order the tasks by the index and add every task's time to the previous task's starttime .

My attempt to solve this:

def create
  @day = current_user.days.build(day_params)
  @day.save

  @day.tasks.each do |task|
    task.index = task.ur**2 + task.imp

  end

  if current_user.worktype = 1
    @tasks = @day.tasks.order(index: :desc)
    x = 0
    @tasks.each do |task|
      if x = 0
        task.starttime = Time.new.beginning_of_day + 8*60*60
        x = task.id
      else
        task.starttime = @day.task.find(x).starttime + @day.task.find(x).time*60
        x = task.id
      end
    end
  elsif current_user.worktype = 2
   ...
  end
  @day.save

  respond_to do |format|
    if @day.save
      format.html { redirect_to @day, notice: 'Day was successfully created.' }
      format.json { render :show, status: :created, location: @day }
    else
      format.html { render :new }
      format.json { render json: @day.errors, status: :unprocessable_entity }
    end
  end
end

But somehow starttime remains nil, when I want to print it out in the view

- @tasks.each do |task|
  ...
  = task.starttime.strftime("%H:%M")

I checked it in rails console too.

consolelog for POST:

Started POST "/days" for ::1 at 2016-08-04 02:19:03 +0200
Processing by DaysController#create as HTML
Parameters: {"utf8"=>"V",  "authenticity_token"=>"YaLq2XBUMltzCpZxvKBp5NQGUgiw/Ockto1r0zy/dZHU3HVlp4lpcsH/b3Q9WYas97ENlwRiPzCUdOiBC06GbA==", "day"=>{"tasks_attributes"=>{"1470269934695"=> {"description"=>"1", "ur"=>"1", "imp"=>"1", "time"=>"1"
, "_destroy"=>"false"}, "1470269939280"=>{"description"=>"2", "ur"=>"3",  "imp"=>"3", "time"=>"2", "_destroy"=>"false"}}}, "commit"=>"Create Day"}
User Load (0.5ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ?   ORDER BY "users"."id" ASC LIMIT 1  [["id", 1]]
 (0.0ms)  begin transaction
SQL (3.5ms)  INSERT INTO "days" ("user_id", "created_at", "updated_at") VALUES (?, ?, ?)  [["user_id", 1], ["created_at", "2016-08-04 00:19:03.986762"],  ["updated_at", "2016-08-04 00:19:03.986762"]]
SQL (0.0ms)  INSERT INTO "tasks" ("description", "ur", "imp", "time", "day_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?, ?, ?)  [["description", "1"], ["ur", 1], ["imp", 1], ["time", 1], ["day_id", 11], ["created_at", "2016-08-04 00:19:03.992775"], ["updated_at", "2016-08-04 00:19:03.992775"]]
SQL (0.0ms)  INSERT INTO "tasks" ("description", "ur", "imp", "time", "day_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?, ?, ?)  [["description", "2"], ["ur", 3], ["imp", 3], ["time", 2], ["day_id", 11], ["created_at", "2016-08-04 00:19:03.994776"], ["updated_at", "2016-08-04 00:19:03.994776"]]
 (4.0ms)  commit transaction
Task Load (0.5ms)  SELECT "tasks".* FROM "tasks" WHERE "tasks"."day_id" = ?  [["day_id", 11]]
Task Load (0.5ms)  SELECT "tasks".* FROM "tasks" WHERE "tasks"."day_id" = ?  ORDER BY "tasks"."index" DESC  [["day_id", 11]]
(0.0ms)  begin transaction
SQL (1.0ms)  UPDATE "tasks" SET "index" = ?, "updated_at" = ? WHERE "tasks"."id" = ?  [["index", 2], ["updated_at", "2016-08-04 00:19:04.006796"], ["id", 24]]
SQL (1.0ms)  UPDATE "tasks" SET "index" = ?, "updated_at" = ? WHERE "tasks"."id" = ?  [["index", 12], ["updated_at", "2016-08-04 00:19:04.009792"], ["id", 25]]
(3.6ms)  commit transaction
(0.0ms)  begin transaction
(0.0ms)  commit transaction
Redirected to http://localhost:3000/days/11
Completed 302 Found in 39ms (ActiveRecord: 14.6ms)

EDIT

Building on @evanbike's answer I added a task.save everytime starttime is set. But nothing changed, so I tried and removed the If statement and now starttime is saved, but every task has the same time.

@tasks = @day.tasks.order(index: :desc)
x = 0
@tasks.each do |task|
  if x = 0
    task.starttime = Time.new.beginning_of_day + 8*60*60
    task.save
    x = task.id
  else
    task.starttime = @day.task.find(x).starttime + @day.task.find(x).time*60
    task.save
    x = task.id
  end
end
@day.save

I hope someone can help me with this issue.
Thanks in advance.

Answer 1

When you do this, you are setting the index on the instance of the task in the @day association cache:

@day.tasks.each do |task|
  task.index = task.ur**2 + task.imp
end

Then, when you do this:

@tasks = @day.tasks.order(index: :desc)

...it makes a db call (since you're calling order on it) and return new instances—that don't have index set. If you called sort or some array method, it would use the stored instances

I think the simplest would be to save the instances of tasks after you set each of the values. Calling sort on the association would probably work, but it seems brittle.