Active Record Associations


  • What is an Association? 
  • Auto-generated methods 
  • How to implement Association? 
  • Cardinality 
  • Eager loading Association

What is and Why Use Associations?

What is an Association? 

  • Represent relationship between database tables, whose relationship is constructed through foreign keys or join table 
    • Examples: "A Customer has many Order's" or "An Order belongs to a Customer". 
  • Cardinality relationship 
    • One-to-one: A person has a single primary address 
    • One-to-many: A school has many students 
    • Many-to-many: A course has many students and each student take many courses

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