ActiveRecord的查询与多个联接不承认的关系
我想写一个ActiveRecord查询,返回就读于一定的疗程用下面的查询所有学生:ActiveRecord的查询与多个联接不承认的关系
def self.students_enrolled_in(course_id)
Student
.joins(:enrollments)
.joins(:sections)
.joins(:courses)
.where(sections: { course_id: course_id })
end
结果在轨控制台:
ActiveRecord::ConfigurationError: Can't join 'Student' to association named 'sections'; perhaps you misspelled it?
它似乎是该协会是作出。我究竟做错了什么?这个查询实际上是否意味着所有的join()
语句都必须与Student关联,或者应该找出关系链接?
教授展示页:
<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>
型号:
招生
class Enrollment < ApplicationRecord
belongs_to :section
belongs_to :student
end
学生:
class Student < ApplicationRecord
has_many :enrollments
end
教授:
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
课程:
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
模式:
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
你过应用.joins
。尝试从内到外尝试。首先,找到课程:
Course.find_by(id: course_id)
然后,找到与course
相关联的所有部分。不需要做这里joins
:
Section.where(course: Course.find_by(id: course_id))
现在,你做你的加入:
Student.joins(:enrollments).where(enrollments: {section: Section.where(course: Course.find_by(id: course_id))})
我认为是应该做的伎俩为您服务。但是,未经测试。所以,给它一个去看看它是否有效。
P.S .:试试只发布最相关的代码。排除一堆无关的东西并不是很有趣。
朋友。
Student .joins(enrollments: [:sections,:courses]) .where(sections: { course_id: course_id })
或
Student .joins(enrollments: [:sections]) .where(sections: { course_id: course_id })
另一种方式做,这是一些协会添加到您的Student
型号:
class Student < ApplicationRecord
has_many :enrollments
has_many :sections, through: :enrollments
has_many :courses, through: :sections
scope :enrolled_in_course, -> (course) { joins(:sections).where(course_id: course.id)
end
然后你可以找到所有学生在course
招收有:
Student.enrolled_in_course(course)
这比接受的答案好得多。 – max
谢谢,我现在会测试它。并不完全确定这种情况下的相关性,如果知道这些实体之间的相关性是否恰当,那么它们就被包括在内。 – StillLearningToCode