Using Database Constraints Wisely

Using databaseconstraints wisely Barun Singh bsingh@wegowise.com Founder & CTO

What is a database? A collection of data that you can read, write, and organizeThe software tools that let you do this

What do we want from a database?It should be …•  Reliable•  Fast•  Secure•  …

A relational database is not the same as a generic data store

What do we want from a relational database?It should be …•  Reliable•  Fast•  Secure•  Sensible•  …

Wait a minute…Is this Rails approved™ ?

The Rails way says…•  You should be database agnostic•  Application layer is the only really important part

The database is important

But why?Because you make mistakes.

What’s the worst that can happen?•  Feature doesn’t work•  Site goes down•  Irrecoverable data loss

I write tests. Why botherwith database constraints?I test my entire application flow throughintegration tests.Why write unit tests?

I write tests. Why botherwith database constraints?My application requires Javascript, and I haveJS validations.Why bother with model-level validations?

Your database has an interface.

How?•  Simple constraints: [not null]•  Unique indices•  Foreign keys [foreigner gem]

It’s not always that simple

Polymorphism Imageable EmployeePicture Product

Polymorphism What does this reference?

Polymorphism

Polymorpheus

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?

PolymorpheusThe gem takes care of all of this for you through a simple migration method

Polymorpheus

Polymorpheus Also provides a validation method,model level validations are still important

You can keep yourapplication logic clean andset up your database properly

Questions?bsingh@wegowise.com

Using Database Constraints Wisely

by barunio on Dec 14, 2011

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Using Database Constraints Wisely — Presentation Transcript