From: Tony Arcieri <tony.arcieri@...>
Date: 2010-12-31T17:07:24+09:00
Subject: Re: Where To Put Validation Logic?

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I think the traditional Rails thinking is going to be: in the model, and
more specifically the Rails 3 thinking is going to be in an
ActiveModel-drived model.

On Thu, Dec 30, 2010 at 8:08 PM, Tom Wardrop <tom@tomwardrop.com> wrote:

> This is probably a question you could put to any programmer who writes
> object-oriented code.
>
> I'm developing a Mongo object mapper for Ruby, inspired by Candy's
> write-on-set approach. I'm currently still in the planning phase, trying
> to work out the scope of the project and the most appropriate interface.
> One question I now find myself asking, is whether to include validation
> helpers, and if so, where should they reside? In the model, or in the
> controller? The answer I guess also depends on the scope of the project.
> Will the mapper act as a foundation for all models (like most mappers),
> or will it be more like a tool that models will simply use, if they have
> to - something I'm still undecided on, but which I'm hoping this thread
> may help me with.
>
> While validation serves as a means to ensure the integrity of data, it
> can also serve as a means to validate user input at the application
> level. If you look at validations as a means to ensure data integrity,
> then naturally, such logic should reside in the model; the data layer of
> the application. On the other hand, looking at validation as a means to
> validate user input and interactions with the UI, you would think the
> controller would be the better fit.
>
> When you think about it, you're really dealing with two types or levels
> of validation: user-level, and data-level. A good example that
> demonstrates this, is assume you had an application that can accept a
> home phone number, a work phone number, and a mobile/cell phone number.
> No field is mandatory, but at least one phone number must be given. You
> could call this multi-field validation. In theory, the data layer of
> your application shouldn't give a damn about whether or not at least one
> phone number is set. All the data layer should care about is whether it
> has a valid phone or not. How I see it, such "multi-field" validation
> can be classed as general application logic which should be the
> responsibility of the view/controller, not the data layer, who's only
> responsible should be persisting the data.
>
> Sadly, I don't know the right answer here, hence why I've come to this
> forum. Hopefully some of you have some thoughts or opinions to share on
> this matter?
>
> Remember, one the main reasons for bringing up this topic, is because
> I'm writing a Mongo object mapper that writes to Mongo when a field is
> set, hence such multi-field validation can't easily be achieved. This
> made me challenge my understanding of validations and which part of the
> application should be responsible for them.
>
> --
> Posted via http://www.ruby-forum.com/.
>
>


-- 
Tony Arcieri
Medioh! Kudelski

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