I have 3 models: User, Order and Car and I have question because I don't know what relationships between these models will be the best. Only requirement is that only one car per user in order.
A user can have many orders, and therefore, many cars through those orders.
class User < ActiveRecord::Base
has_many :orders
has_many :cars, through: :orders
end
An order belongs to a user and a car.
class Order < ActiveRecord::Base
belongs_to :user
belongs_to :car
end
A car has one order.
class Car < ActiveRecord::Base
has_one :order
end
So you need one on one relationship between order and car and then back to order and customer one relationship. Something below should do the trick.
class Car < ActiveRecord::Base
has_one :order
has_one :customer, through: :order
end
class Order < ActiveRecord::Base
belongs_to :car
belongs_to :customer
end
class Customer < ActiveRecord::Base
has_one :order
has_one :car , through: :order
end
But i will suggest the has_many relationship by the looks of the model name, but you know better your problem than me.
Related
Here is my models:
class User < ActiveRecord::Base
has_many :products
has_many :comments
end
class Product < ActiveRecord::Base
belongs_to :user
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :user
belongs_to :product
end
I need to get comment records from current user products only
How do I do that? thanks
If we move the relationships to use a has_many: comments, through: products you can probably get what you're after:
class User < ActiveRecord::Base
has_many :products
has_many :comments, through: products
end
class Product < ActiveRecord::Base
belongs_to :user
has_many :comments
end
class Comment < ActiveRecord::Base
belongs_to :user
belongs_to :product
end
Now you can do user.comments.
The rails docs are here, which say:
A has_many :through association is often used to set up a many-to-many
connection with another model. This association indicates that the
declaring model can be matched with zero or more instances of another
model by proceeding through a third model. For example, consider a
medical practice where patients make appointments to see physicians.
I have four models
Bid Order User Printer
currently I cannot access the order through anything except User.
I would like to be able to do something of the sort bid.order but have yet to figure out the correct association. Any thoughts?
class Bid < ActiveRecord::Base
belongs_to :printer
end
class Order < ActiveRecord::Base
belongs_to :user
has_many :bids
end
class Printer < ActiveRecord::Base
has_many :orders, through: :bids
has_many :bids
end
class User < ActiveRecord::Base
has_many :orders
end
Both models must know about the relationship so you need to state that in the Bid model
class Bid < ActiveRecord::Base
belongs_to :printer
belongs_to :order
end
I have a many-to-many relationship setup for Teachers and Classrooms via has_many :through:
class Teacher < ActiveRecord::Base
has_many :classrooms, :through => :classroom_memberships
end
class Classroom < ActiveRecord::Base
has_many :students
has_many :teachers, :through => :classroom_memberships
end
class ClassroomMemberships < ActiveRecord::Base
belongs_to :teacher
belongs_to :classroom
end
Currently, Students can only belong to one Classroom:
class Student < ActiveRecord::Base
belongs_to :classroom
end
Now I have the need to track historical classroom memberships for students, creating a second many-to-many relationship for classrooms. So, while a student can only belong to one classroom at a time, I need to know that last year, student A belonged to classroom B.
I'm thinking I have two viable options:
1.) Make the classroom_memberships association polymorphic so I'd have a classroomable_id and classroomable_type that would point to either a teacher OR a student.
2.) Simplify things and add another foreign key to ClassroomMemberships called student_id, in which case, for a given row, either student_id OR teacher_id would have a value.
Which is the better option?
I would probably go the route of:
class Course < ActiveRecord::Base
# like "MATH 100"
has_many :sections
has_many :teachers, :through => :sections
end
class Term < ActiveRecord::Base
# like "Fall 2015"
has_many :sections
end
class Teacher < ActiveRecord::Base
has_many :sections
has_many :courses, :through => :sections
end
class Section < ActiveRecord::Base
# a course, in a term, taught by a teacher, with registered students
belongs_to :term
belongs_to :course
belongs_to :teacher
has_many :registrations
has_many :students, :through => :registrations
end
class Registration < ActiveRecord::Base
# a student in a specific section
belongs_to :section
belongs_to :student
end
class Student < ActiveRecord::Base
# a student's registrations are their course history
has_many :registrations
has_many :sections, through :registrations
end
As a start, since this is a fairly basic modeling of an educational system.
It sounds like maybe you want a ClassroomMembershipHistory model.
Something like
class ClassroomMembershipHistory < ActiveRecord::Base
belongs_to :student
belongs_to :classroom
end
with a year attribute, stored however is easiest to query for your use case.
I'm a beginner in Rails and I have a problem with ActiveRecords associations.
I'm creating simple car rental service and I made the following associations:
class Client < ActiveRecord::Base
has_many :rentals
has_many :bookings
has_many :cars, :through => :rentals
has_many :cars, :through => :bookings
end
class Rental < ActiveRecord::Base
belongs_to :client, dependent: :destroy
has_one :car
end
class Booking < ActiveRecord::Base
belongs_to :client, dependent: :destroy
has_one :car
end
What I need is to have a car belonging to many bookings and rentals while every booking and rental can have only one car assigned.
class Car < ActiveRecord::Base
# belongs_to_many :bookings
# belongs_to_many :rentals
end
How should I do that?
If a car can have many bookings/rentals, but a booking/rental can only have one car, you're looking at a classic belongs_to/has_many situation. It looks like you're being tripped up by the distinction between belongs_to and has_one -- it's not a grammatical one, but a matter of where the foreign key column is located in your database.
belongs_to: "I am related to exactly one of these, and I have the foreign key."
has_one: "I am related to exactly one of these, and it has the foreign key."
has_many: "I am related to many of these, and they have the foreign key."
Note that has_one and has_many both imply there's a belongs_to on the other model, since that's the only option where "this" model has the foreign key. Note also that this means has_one should only be used when you have a one-to-one relationship, not a one-to-many.
Taking this into consideration, I would replace the has_one :car with belongs_to :car in both your Rental and Booking models, and place has_many :bookings and has_many :rentals in your Car model. Also ensure that your rentals and bookings tables have a car_id column; there should be no rental- or booking-related columns in your cars table.
Yes, there is a "belongs_to_many" in Rails, sort of. It's a little more work and you can't use generators with it. It's called a polymorphic association.
Even though you could make a car have many bookings & rentals, you could associate the car by making it belong to a polymorph such as rentable_vehicle. Your code would look like this
class Car < ActiveRecord::Base
belongs_to :rentable_vehicle, polymorphic: true
end
class Rental < ActiveRecord::Base
belongs_to :client, dependent: :destroy
has_many :cars, as: :rentable_vehicle
end
class Booking < ActiveRecord::Base
belongs_to :client, dependent: :destroy
has_many :cars, as: :rentable_vehicle
end
You can't do belongs_to_many. The closest you can really get is has_and_belongs_to_many, but I'm not sure that's what you want here - unless you can have multiple cars per rental/booking. Check out the guide for a full explanation.
I'd change it up like this:
class Rental < ActiveRecord::Base
belongs_to :client, dependent: :destroy
belongs_to :car
end
class Booking < ActiveRecord::Base
belongs_to :client, dependent: :destroy
belongs_to :car
end
class Car < ActiveRecord::Base
has_many :bookings
has_many :rentals
end
Also, I don't know how your rentals relate to bookings, but my immediate thought is that there should be some relationship between the two, because you probably can't have a rental without booking it, right?
In my rails application Company acts as the user model. A company can have many customers and many employees (carseller).
There is a many to many relation between a carseller and a customer.
There is the following problem: A lot of times i'd have to retrieve all the appointments made with the whole company. Since there is no company_id saved in the appointment model this can be quite painful.
Should i just include a foreign key to company in the appointments and have some form of redundancy or is there another easy and efficient way?
class Company < ActiveRecord::Base
has_many :customers
has_many :carseller
end
class Customer < ActiveRecord::Base
belongs_to :company
has_many :appointments
has_many :carsellers, :through => :appointments
end
class Carseller < ActiveRecord::Base
belongs_to :company
has_many :appointments
has_many :customers, :through => :appointments
end
class Appointment < ActiveRecord::Base
belongs_to :customer
belongs_to :carseller
end
I think you can use :
class Appointment < ActiveRecord::Base
belongs_to :customer
belongs_to :carseller
has_one :company, :through => :carseller
end
Then you just have to do appointment.company to get it.