Using Database Constraints Wisely

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