Rendering the result of a controller method to a partial in the view

I have this Rails code in a method in a controller. It takes four parameters, does a bit of math and I'd like it to return a the value stored in the 'attendance' variable to a partial in a view.

def find_attendance(lesson_id, student_id, start_date, end_date)
    marks = Array.new

    all_registers = Register.where(:lesson_id => lesson_id)

    start_date.upto(end_date) do |date|
        all_registers.each do |register|
            if date == register.date
                this_mark = RegisterMark.where(:student_id => student_id, :register_id => register.id)
                this_mark.each do |mark|
                    marks << mark.mark
                end
            end
        end
    end

    attendance = ((Float(marks.count("O")) + Float(marks.count("N"))) / Float(marks.count)) * Float(100)
end

I have created a _find_attendance.ht开发者_如何学运维ml.erb file in the relevant view directory, and tried calling the partial by using <%= render :partial => "find_attendance" %> but I'm having trouble passing parameters and using the correct variable name within the partial.

I've tried playing around with using instance variables on 'attendance'.

Any pointers?

---

The first thing you need to do is put the values that you want to pass to your views (regular views and partial views) into a controller variable, like this:

@attendance = ((Float(marks.count("O")) + Float(marks.count("N"))) / Float(marks.count)) * Float(100)

Next, you'll need to rename your partial something other than find_attendance. That's the name of the view for the find_attendance action, and if I understand your question, you want that view (find_attendance.html.erb) to call a partial with the attendance. So, try something like this:

find_attendance.html.erb:
<%= render :partial => "attendance", :object => @attendance %>

Now, inside the partial _attendance.html.erb, you can refer to an instance variable attendance. (Partials assume the existence of an instance variable with the same name as the partial; that's the :object we passed through render.

_attendance.html.erb:
<p>Attenance: <%= attendance %></p>

---

You almost certainly want to add this method as a method to the model. Maybe in your case the lesson model?

class Lesson < ActiveRecord::Base

  has_many :registers

  def calculate_attendance_for_student(student, start_date, end_date)
    valid_dates = start_date.upto(end_date)   
    registers.each do |register|
    ...
  end
end

Then in your view you can get at the @lesson model to get attendance.

There's some area for improvement in your loops, I included a simple way to loop through all Register for a Lesson above. You can do this for both your Register.where and your RegisterMark.where for speed improvements