Je suis en train d'écrire un ActiveRecord requête qui retourne tous les étudiants inscrits à un certain cours avec la requête suivante:requête ActiveRecord avec des jointures multiples ne reconnaissant pas les relations
def self.students_enrolled_in(course_id)
Student
.joins(:enrollments)
.joins(:sections)
.joins(:courses)
.where(sections: { course_id: course_id })
end
le résultat dans la console Rails est:
ActiveRecord::ConfigurationError: Can't join 'Student' to association named 'sections'; perhaps you misspelled it?
il semble que l'association est faite. Qu'est-ce que je fais mal? la requête signifie-t-elle réellement que toutes les instructions join()
doivent se rapporter à Student, ou devrait-elle retracer les liens relationnels?
Professeur page show:
<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>
modèles:
inscription
class Enrollment < ApplicationRecord
belongs_to :section
belongs_to :student
end
étudiants:
class Student < ApplicationRecord
has_many :enrollments
end
Professeur:
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
Cours:
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
Schéma:
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
merci, je vais le tester maintenant. n'était pas exactement sûr de ce qui était pertinent dans ce cas, si savoir comment les entités étaient liées était pertinent ou non, de sorte qu'ils ont été inclus. – StillLearningToCode