August 21, 2014

Rails 4 Association has_many, through

##Setup

A hospital has physicians and patients. A physician has many patients. A patient has many physicians. They two parties meet via appointments. Appointments have a date, time, location, patient, and physician.

Patient needs: Do I have any physician appointments? When, where, & with whom?
Physician needs: Do I have any appointments today? Show me each appointment location, time, and name of each patient.

In your shell…

rails new hospital
cd hospital
rails generate scaffold physician name:string
rails generate scaffold patient name:string
rails generate scaffold appointment location:string date:date time:time physician:references patient:references

Go to your models and make ‘em look like this…

class Physician < ActiveRecord::Base
  has_many :appointments
  has_many :patients, :through => :appointments
end

class Patient < ActiveRecord::Base
  has_many :appointments
  has_many :patients, :through => :appointments
end

class Appointment < ActiveRecord::Base
  belongs_to :physician
  belongs_to :patient
end

Open up your controllers, scroll down to the bottom and check out your strong parameters. Physician and Patient are only allowed to write :title. Look at the appointments_controller. Note the :physician_id and the :patient_id.

params.require(:appointment).permit(:physician_id, :patient_id, :location, :date, :time)

Migrate your database

rake db:migrate

and make some data in the console.

rails c
dr_fred = Physician.create!(name: "Dr. Fred")
dr_cindy = Physician.create!(name: "Dr. Cindy")

paitent_bob = Patient.create!(name: "Bob the Patient")
patient_sue = Patient.create!(name: "Sue the Patient")

Appointments establish the association with the physician_id and patient_id. Check out the ids.

dr_fred.id  #=>1
dr_cindy.id #=>2
patient_bob.id #=>1
patient_sue.id #=>2

Bob wants to make an appointment with Dr. Cindy at the hospital today.

an_appointment = Appointment.create!(physician_id: 1, patient_id: 2, date: Date.today, time:Time.now, location: "The Hospital")

And where done! Here are a few ways to check out your data in the console.

dr_fred.appointments.where(date: Date.today).count  #=>1
dr_fred.appointments.where(date: Date.tomorrow).count  #=>0

patient_sue.appointments.first.physician.name  #=>"Dr Fred"

References

Inspired by has_and_belongs_to_many relationship in Rails 4.x.

The scenario is based on the example on guides.rubyonrails.org

Rails 4 Association has_many, through

References

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