A blog about software by Alexander Yaäkov Garber.

ActiveRecord Associations

rails database sql
Published on 27 Mar 2020

This is a simple explanation of some basic concepts of Active Record Assocations.

School Example

We have the following entities:

  1. Classroom
  2. Teacher
  3. Pupil
  4. Subject

Active Record Assocations


Classroom has_one :teacher
Teacher belongs_to :classroom

Teacher has_many :courses
Course belongs_to :teachers

Course has_and_belongs_to_many :pupils
Pupil has_and_belongs_to_many :courses

Database Tables

classrooms
id
room_number
teachers foreign_key
id  
name  
classroom_id classrooms.id
courses foreign_key
id  
title  
teacher_id teachers.id
pupils
id
name
course_pupils foreign_key
pupil_id pupils.id
course_id courses.id

related posts

all tags

activerecord android annoyances api apt arch array artix atom az3w backend bash blog browser bug callback career cli cloud code coding config configuration cp crud css database db design devops django email erp filter fugitive gif gist git gnome grep hebrew http ide isbn-fetcher iso javascript job search js kanban kanban\ kindle koans linux logger manjaro map markdown microservices mobi mtp neovim nodejs packages pastbin patch post python rails reduce refactoring rest routes rspec ruby scripting security sed shell sql string_replacement study tdd terminal testing version_control vim walkthrough workflow