Passing instance variable from Model to View to Controller in Rails

Question

Basic app. Trying to make a button that clicks and shows the next page in this case lesson.

In my controller I have:

def show 
  @lesson = Lesson.find(params[:id])
end 

In my view (show.html.erb) I have:

...
<p><%= link_to 'Previous', Lesson.previous(@lesson) %></p>
<p><%= link_to 'Next', Lesson.next(@lesson) %></p>
...

In my model I have:

def self.next(current_lesson)
  current_lesson.number + 1
end

def self.previous(current_lesson)
  current_lesson.number - 1
end 

My schema includes a number column that is an integer.

However, this errors out with 'undefined method `to_model' for 0:Fixnum' and when I run @lesson in the console, it comes up as nil.

I also tried this:

def self.next
  current_lesson = Lesson.find(@lesson.id)
  next_lesson = current_lesson.number + 1 
end 

def self.previous 
  current_lesson = Lesson.find(@lesson.id)
  previous_lesson = current_lesson.number - 1
end

This however, successfully passes the model the instance variable because in the console @lesson returns the correct value but it cannot call the method.

thoughts?

Edit: another solution attempted:

I tried changing this to an instance method rather than a class method. So in the view I set @lesson.previous and @lesson.next. In the model I did this:

def next
  self.number + 1
end 

def previous
  self.number - 1
end

But alas, I get @instance nil error again.

Answer 1

self.next & self.previous return integer instead of Lesson. Make them return next and previous Lesson objects and it should work. Ie

    Lesson.find_by_number(self.number-1)

Answer 2

In the function

def self.next
  current_lesson = Lesson.find(@lesson.id)
  next_lesson = current_lesson.number + 1
end

you will return a Fixnum instead of a Lesson object.

If you want to return a Lesson with an id 1 higher you are probably better off doing something like:

def next
  Lesson.find(self.number + 1)
end

Answer 3

The reason why you're getting the error is that Lesson.next and Lesson.previous return integers and not lesson objects. If you wanted to continue using the next and previous class methods, you could make the following change in your view

<p><%= link_to 'Previous', lesson_path(Lesson.previous(@lesson)) %></p>
<p><%= link_to 'Next', lesson_path(Lesson.next(@lesson)) %></p>