Using Database Constraints Wisely

Transcript

1. Using database constraints wisely Barun Singh bsingh@wegowise.com Founder & CTO

2. What is a database? A collection of data that you

   can read, write, and organize The software tools that let you do this

3. What do we want from a database? It should be

   … •  Reliable •  Fast •  Secure •  …

4. A relational database is not the same as a generic

   data store

5. A relational database is not the same as a generic

   data store

6. What do we want from a relational database? It should

   be … •  Reliable •  Fast •  Secure •  Sensible •  …

7. Wait a minute… Is this Rails approved™ ?

8. The Rails way says… •  You should be database agnostic

   •  Application layer is the only really important part

9. The database is important

10. But why? Because you make mistakes.

11. What’s the worst that can happen? •  Feature doesn’t work

    •  Site goes down •  Irrecoverable data loss

12. I write tests. Why bother with database constraints? I test

    my entire application flow through integration tests. Why write unit tests?

13. I write tests. Why bother with database constraints? My application

    requires Javascript, and I have JS validations. Why bother with model-level validations?

14. Your database has an interface.

15. How? •  Simple constraints: [not null] •  Unique indices • 

    Foreign keys [foreigner gem]

16. It’s not always that simple

17. Polymorphism Imageable Picture Employee Product

18. Polymorphism What does this reference?

19. Polymorphism

20. Polymorpheus

21. A couple little snags… How can you make sure that

    one picture has only an employee_id or product_id but not both? (xor constraints are tough) And what if the polymorphic relationship has to be unique?

22. Polymorpheus The gem takes care of all of this for

    you through a simple migration method

23. Polymorpheus The gem takes care of all of this for

    you through a simple migration method

24. Polymorpheus

25. Polymorpheus Also provides a validation method, model level validations are

    still important

26. You can keep your application logic clean and set up

    your database properly

27. Questions? bsingh@wegowise.com