custom query in active record with multiple joins - ruby-on-rails

Question

I am very new to rails and active record so I'm probably doing something wrong, but... using the schema below, I want to create a list of courses in the outer do loop, then list each student enrolled in the course with the inner do loop. I m not sure if this approach will work, but this error keeps popping up:
ActionView::Template::Error (undefined method `enrollments' for #):
it seems that the association is made. what am i doing wrong?
Professor show page:
<div class="col-md-8">
<h2 class="card-title"><%= #professor.name %></h2>
<% #courses_taught.each do |course| %>
<div class="card mb-4 card-header">
<img class="card-img-top" src="http://placehold.it/750x300" alt="Card image cap">
<h3 class="card-text"><%= course.title %></h3>
</div>
<div class="card-body">
<% course.sections.enrollments.students.each do |student| %>
<p><% student.name %></p>
<% end %>
</div>
<% end %>
</div>
models:
enrollment
class Enrollment < ApplicationRecord
belongs_to :section
belongs_to :student
end
Student:
class Student < ApplicationRecord
has_many :enrollments
end
Professor:
class Section < ApplicationRecord
has_many :enrollments
belongs_to :professor
belongs_to :course
validates_uniqueness_of :professor_id, scope: :course_id
scope :by_professor_id, ->(prof_id) { where('professor_id = ?', prof_id) }
end
Course:
class Course < ApplicationRecord
enum status: { planning: 0, offered: 1 }
scope :offered, -> { where(status: 1) }
scope :planning, -> { where(status: 0) }
belongs_to :department
has_many :sections
has_many :professors, through: :sections
validates :title, :number, :status, :description, presence: true
validates :description, length: { in: 10..500 }
validates :title, :number, uniqueness: { case_sensitive: false }
def self.search(term)
if term
where('title LIKE ?', "%#{term}%").order('title DESC')
else
order('title ASC')
end
end
def self.taught_by(professor_id)
Course
.joins(:sections)
.joins(:professors)
.where(sections: { professor_id: professor_id })
.select('distinct courses.*')
end
end
Schema:
ActiveRecord::Schema.define(version: 20171013201907) do
create_table "courses", force: :cascade do |t|
t.string "title"
t.text "description"
t.string "number"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "status", default: 0
t.integer "department_id"
t.index ["department_id"], name: "index_courses_on_department_id"
end
create_table "departments", force: :cascade do |t|
t.string "name"
t.text "description"
t.text "main_image"
t.text "thumb_image"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "enrollments", force: :cascade do |t|
t.integer "section_id"
t.integer "student_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.index ["section_id"], name: "index_enrollments_on_section_id"
t.index ["student_id"], name: "index_enrollments_on_student_id"
end
create_table "professors", force: :cascade do |t|
t.string "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "status", default: 0
t.integer "department_id"
t.text "bio"
t.index ["department_id"], name: "index_professors_on_department_id"
end
create_table "sections", force: :cascade do |t|
t.integer "number"
t.integer "max_enrollment"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "professor_id"
t.integer "course_id"
t.string "room"
t.index ["course_id"], name: "index_sections_on_course_id"
t.index ["professor_id", "course_id"], name: "index_sections_on_professor_id_and_course_id", unique: true
t.index ["professor_id"], name: "index_sections_on_professor_id"
end
create_table "students", force: :cascade do |t|
t.string "name"
t.decimal "gpa"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "users", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "name"
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.integer "sign_in_count", default: 0, null: false
t.datetime "current_sign_in_at"
t.datetime "last_sign_in_at"
t.string "current_sign_in_ip"
t.string "last_sign_in_ip"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.string "roles"
t.index ["email"], name: "index_users_on_email", unique: true
t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
end
end

Answer 1

enrollment belongs_to user, there is no need to use each on single record rather it will throw error. You can use below code.
<% course.sections.each do |section| %>
<% section.enrollments.each do |enrollment| %>
<p><% enrollment.student.name %></p>
<% end %>
<% end %>

Answer 2

Sean's answer is almost correct but since enrollments belongs_to student
you would use the singular form enrollment.student. but more simply you can just call student from inside enrollments block.
<div class="col-md-8">
<h2 class="card-title"><%= #professor.name %></h2>
<% #courses_taught.each do |course| %>
<div class="card mb-4 card-header">
<img class="card-img-top" src="http://placehold.it/750x300" alt="Card image cap">
<h3 class="card-text"><%= course.title %></h3>
</div>
<div class="card-body">
<% course.sections.each do |section| %>
<% section.enrollments.each do |enrollment| %>
<p><% enrollment.student.name %></p>
<% end %>
<% end %>
</div>
<% end %>
</div>

Answer 3

<div class="col-md-8">
<h2 class="card-title"><%= #professor.name %></h2>
<% #courses_taught.each do |course| %>
<div class="card mb-4 card-header">
<img class="card-img-top" src="http://placehold.it/750x300" alt="Card image cap">
<h3 class="card-text"><%= course.title %></h3>
</div>
<div class="card-body">
<% course.sections.each do |section| %>
<% section.enrollments.each do |enrollment| %>
<p><% enrollment.student.name %></p>
<% end %>
<% end %>
</div>
<% end %>
</div>