Comments on: When should I validate in controllers and not in models?

By: Why you should validate in your controllers and not your models | A Foolish Manifesto

Thu, 18 Jun 2009 04:29:34 +0000

[...] I got some responses based on my question yesterday about why validation shouldn’t be in the model of an MVC-based [...]

By: Amiri

Amiri — Wed, 17 Jun 2009 21:35:06 +0000

An email address seems like something that could easily go in the model, and should. The “earlier” it is handled, the better. I guess there are types of validation where the line gets more fuzzy.

By: David E. Wheeler

David E. Wheeler — Wed, 17 Jun 2009 15:04:32 +0000

Because you should do validation in the database. This is one of the primary things a relational database is designed to do, so take advantage of it!

Theory

By: Dave Sherohman

Dave Sherohman — Wed, 17 Jun 2009 10:47:03 +0000

I’ve seen a lot of people using different definitions of what’s a “model” and what’s a “controller”, so this could just be a terminology mismatch.

As I use the terms, in the context of a web app, the “model” includes all of the underlying business classes and the “controller” is responsible solely for mapping data from the model into the view (templates) to generate a page. Under that usage, then, yes, all validation is the model’s job.

To someone else, though, the “model” may only be the database (and perhaps a thin OO layer around it), while the classes encapsulating business rules fall into their definition of “controller”. By those definitions, validation clearly falls into the controller’s realm. (If you’re using Catalyst with “model” classes that have been auto-generated by DBIC from your database schema without having added methods to them that go beyond simple database pass-through accessors, then you’re probably using these definitions.)

What really matters is that you know where your invariant rules and logic – the things which would apply to all applications in the system if you were to write more than one – live. All non-application-specific validation should go there also, regardless of whether you call it a “model” or a “controller”.

By: Zbigniew Lukasiak

Zbigniew Lukasiak — Wed, 17 Jun 2009 08:40:56 +0000

Important part of the problem are the error messages, for the display you need different messages than for the back end. I guess you could have a dictionary to translate them (and that would also be a good start for i18n) – but that’s additional complication. I think the advice to have model side validation is a good one – but it needs a lot of infrastructure to make it usable.

By: Moritz Onken

Moritz Onken — Wed, 17 Jun 2009 05:59:47 +0000

Because the model is not aware of the current user.
Depending on her locale the format of Date/Time inputs is different. Depending on his roles, he may or may not set or change columns.