example of controller code that has been bloated by needing to check many query parameters

courses_controller.rb

class CoursesController < ApplicationController  
  def index
    @semesters = Semester.all
    @courses = Course.all
    if params[:search].present?
      @courses = @courses.search(params[:search])
    end
    if params[:semester].present?
      @courses =
        @courses.joins(:course_instances)
        .where(course_instances: { semester_id: params[:semester].to_i })
    end
    if params[:professor].present?
      professor = Professor.arel_table
      @courses =
        @courses.joins(course_instances: :professor)
        .where(professor[:name].matches("%#{params[:professor]}%"))
    end
    course_ids = @courses.pluck('courses.id').uniq
    @courses = Course.where('id IN (?)', course_ids).order_by_short_name
    @courses = @courses.page(params[:page])
  end
end