# MVC and modules. Views telling models to behave

**URL:** <https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966>\
**Category:** Rails\
**Created:** [October 20, 2006, 6:42am UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966 "2006-10-20T06:42:42Z")\
**Posts on this page:** 8\
**Page:** 1

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 20, 2006, 6:42am UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/1 "2006-10-20T06:42:42Z")

</div>

I was thinking today, it would be nice if a view could tell a model how  
to  
format it’s data for that particular view.

Kind of like, the view is bestowing instant, and temporary knowledge on  
the  
model for the duration of the views run.

It seemed to me that this would be more objecty than say a helper that  
formats a string  
format\_my\_string( my\_string )

Instead, in my view. Lets assume I have a Building class that has a  
phone\_number field

At the top of my view then

\<% Building.include PhoneNumberFormat %\>

The PhoneNumberFormat module could overwrite the getter methods of  
phone\_number, fax\_number etc to provide me with some nice formatting.  
Presumably I could also pass some parameters somewhere (not quite sure  
yet)  
so that I could tell the PhoneNumberFormat what kind of format I want.

Then my building objects, when I call  
\<%= @building.phone\_number -%\>  
instead of  
\<%= format\_my\_phone\_number( @building.phone\_number ) -%\>  
to get the format that I want

Is this a nasty abuse of MVC?

Thanx for any pointers

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 8:33am UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/2 "2006-10-26T08:33:36Z")

</div>

Daniel N wrote:

> Instead, in my view. Lets assume I have a Building class that has a
> 
> Then my building objects, when I call  
> \<%= @building.phone\_number -%\>  
> instead of  
> \<%= format\_my\_phone\_number( @building.phone\_number ) -%\>  
> to get the format that I want
> 
> Is this a nasty abuse of MVC?

Yes!

In MVC, the model provides its data in neutral form and the view decides  
how to present it. This is a clean separation of concerns (and  
separation of concerns is one of the cornerstones of object  
orientation).

In your proposal, the model has to cater for a variety of ways of  
returning each of its attributes (these would all have to be able to  
vary independently) and the view has to know how to program the model to  
give the attribute values in the form you want.

Then what happens when you want a new format, that hadn’t been  
anticipated by the model? You have to:

- add the new formatting capability to the model

- add the ability to switch to that format in the model

- do that switching in the view.

Bear in mind that there’s practically no limit to the different ways in  
which data may be presented (graphical as well as textual), and it  
should be crystal clear that putting the knowledge of how to do this in  
the model is a recipe for disaster.

regards

Justin F.

---

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 9:01am UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/3 "2006-10-26T09:01:39Z")

</div>

Thanx for the feedback. I’ve responded below.

Cheers

On 10/26/06, Justin F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> how to present it. This is a clean separation of concerns (and  
> separation of concerns is one of the cornerstones of object orientation).
> 
> In your proposal, the model has to cater for a variety of ways of  
> returning each of its attributes (these would all have to be able to  
> vary independently) and the view has to know how to program the model to  
> give the attribute values in the form you want.

This would be via the include statement

\<% Building.include PhoneNumberFormat %\>

The model knows nothing of formatting until the very last instant. Then  
immediately forgets at the end of the response cycle. Since the view is  
last, this is effectively; immediately forgets.

Then what happens when you want a new format, that hadn’t been

> anticipated by the model? You have to:
> 
> - add the new formatting capability to the model

Add a new format to the mixin module, not the model

- add the ability to switch to that format in the model

The view would control which module is mixed in at runtime. This  
doesn’t  
need to be done in the model at all as far as I can tell.

- do that switching in the view.

> Bear in mind that there’s practically no limit to the different ways in  
> which data may be presented (graphical as well as textual), and it  
> should be crystal clear that putting the knowledge of how to do this in  
> the model is a recipe for disaster.

Perhaps your right. I was thinking along the lines of a form builder.  
I  
can (& I believe should) have a form defined in a view something like

\<% form\_for :user, :builder =\> MyBuilder do |f| %\>  
\<%= f.text\_field :name %\>  
\<%= f.text\_field :email %\>  
\<%= f.password\_field :password %\>  
\<%= f.password\_field :password\_confirmation %\>  
\<% end %\>

I can have the builder generate whatever I like. I can even select the  
builder programatically if I want.  
I can have that form rendered as a table, or as divs, spans whatever.  
All I  
need to do is build the builder the way I want. Then all my forms  
across  
the site are consistant.

My thinking was along the lines of this. If you have a DateFormatter  
module  
and you could tell it to format all dates of a model a particular way.

Again the syntax is not correct at the moment but something like this  
inside  
a view or in the views helper.

\<% MyModel.include DateFormatter do %\>  
\<% date\_fields :all, “%d %m %y” %\>  
\<% end %\>

I’m not sure how any of the issues that you raised are a problem. Not  
saying they’re not… Just I don’t understand how they are yet.

---

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 9:59am UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/4 "2006-10-26T09:59:42Z")

</div>

On 10/19/06, Daniel N [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Instead, in my view. Lets assume I have a Building class that has a
> 
> >

I just did this for fun, so don’t take this as a recommendation to  
actually start using it or something 🙂

class Person  
attr\_reader :phone

def initialize(phone)  
@phone = phone  
end  
end

module PhoneFormatter  
def self.extended(o)  
(class \<\< o; self; end).instance\_eval do  
alias\_method :old\_phone, :phone  
define\_method(:phone) {  
old\_phone.gsub(/([0-9]{1,3})([0-9]{3})([0-9]{4}$)/,“(\1) \2-\3”)}  
end  
end  
end

irb(main):017:0\> p = Person.new “5555551234”  
=\> #\<Person:0x323eb0 @phone=“5555551234”\>  
irb(main):018:0\> p.phone  
=\> “5555551234”  
irb(main):019:0\> p.extend PhoneFormatter  
=\> #\<Person:0x323eb0 @phone=“5555551234”\>  
irb(main):020:0\> p.phone  
=\> “(555) 555-1234”  
irb(main):021:0\> p.old\_phone  
=\> “5555551234”

The PhoneFormatter module is pretty simple, but I’ll explain it if you  
don’t know the metaprogramming going on. When anything extends PF,  
the extended method gets called and is passed the object (usually a  
class) that was extended with PF. In this case, however, we’re  
extending a Person object rather than the class itself. So then we  
get the metaclass of the person object, make an alias to keep the old  
phone method, and then define a new phone method that applies some  
formatting to the number returned from the old phone method.

In a nutshell, we’re defining a couple singleton methods on p. So it  
won’t affect any other instances of Person.

As I said, I just did that for fun. The main drawback I can  
immediately see is that it doesn’t follow Rails conventions. To be  
honest though I don’t see a whole lot of upside to it…maybe if you  
had several methods you wanted to format differently I guess, you  
could just knock em off in one fell extend rather than calling a bunch  
of helpers.

Maybe someone else would be willing to discuss the pros and cons of my  
approach (which I’ve never used, and don’t intend to). I just decided  
to experiment, and I need my sleep 🙂

Pat

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 12:15pm UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/5 "2006-10-26T12:15:48Z")

</div>

It seem that what you are after is some kind of presenter object. Take  
a look at this article:

> **[Rails Model View Controller + Presenter?](http://blog.jayfields.com/2006/09/rails-model-view-controller-presenter.html)**
>
> Ruby on Rails directs you to use Model View Controller by convention. This often results in a one to many relationship between Controllers ...

---

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 2:33pm UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/6 "2006-10-26T14:33:53Z")

</div>

On 10/26/06, Pat M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> def initialize(phone)  
> end  
> =\> “(555) 555-1234”  
> formatting to the number returned from the old phone method.
> 
> In a nutshell, we’re defining a couple singleton methods on p. So it  
> won’t affect any other instances of Person.

Wow… Thanx for the effort. I see that the extended method in the  
documentation is not yet documented so this is indeed good to see it in  
action.

As I said, I just did that for fun. The main drawback I can

> immediately see is that it doesn’t follow Rails conventions. To be  
> honest though I don’t see a whole lot of upside to it…maybe if you  
> had several methods you wanted to format differently I guess, you  
> could just knock em off in one fell extend rather than calling a bunch  
> of helpers.

I guess one of the main things that I’m thinking of is locale specific  
formatting. Dates, currency, Time, Phone numbers etc. The upside being  
mainly consistency across a view, and DRYness for choosing what that  
format  
is. Specific formatting requirements wouldn’t need to be scattered  
throughout code.

Mainly though it’s just a thought that I was having that I wanted to get  
some perspective on.

Maybe someone else would be willing to discuss the pros and cons of my

> approach (which I’ve never used, and don’t intend to). I just decided  
> to experiment, and I need my sleep 🙂

I guess the only reason that I have been able to think of that this  
might  
not be a good idea, is when some method expects plain responses from a  
model, but recieves the formatted version instead. An adjacent method  
in  
the model for example, or in a different model/controller/helper/module  
may  
blow up in this situation.

---

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 9:09am UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/7 "2006-10-26T09:09:39Z")

</div>

Thanx for the feedback. I’ve responded below.

Cheers

Sorri if this is a double post. I got a message to say that it wasn’t  
delivered.

On 10/26/06, Justin F. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> how to present it. This is a clean separation of concerns (and  
> separation of concerns is one of the cornerstones of object orientation).
> 
> In your proposal, the model has to cater for a variety of ways of  
> returning each of its attributes (these would all have to be able to  
> vary independently) and the view has to know how to program the model to  
> give the attribute values in the form you want.

This would be via the include statement

\<% Building.include PhoneNumberFormat %\>

The model knows nothing of formatting until the very last instant. Then  
immediately forgets at the end of the response cycle. Since the view is  
last, this is effectively; immediately forgets.

Then what happens when you want a new format, that hadn’t been

> anticipated by the model? You have to:
> 
> - add the new formatting capability to the model

Add a new format to the mixin module, not the model

- add the ability to switch to that format in the model

The view would control which module is mixed in at runtime. This  
doesn’t  
need to be done in the model at all as far as I can tell.

- do that switching in the view.

> Bear in mind that there’s practically no limit to the different ways in  
> which data may be presented (graphical as well as textual), and it  
> should be crystal clear that putting the knowledge of how to do this in  
> the model is a recipe for disaster.

Perhaps your right. I was thinking along the lines of a form builder.  
I  
can (& I believe should) have a form defined in a view something like

\<% form\_for :user, :builder =\> MyBuilder do |f| %\>  
\<%= f.text\_field :name %\>  
\<%= f.text\_field :email %\>  
\<%= f.password\_field :password %\>  
\<%= f.password\_field :password\_confirmation %\>  
\<% end %\>

I can have the builder generate whatever I like. I can even select the  
builder programatically if I want.  
I can have that form rendered as a table, or as divs, spans whatever.  
All I  
need to do is build the builder the way I want. Then all my forms  
across  
the site are consistant.

My thinking was along the lines of this. If you have a DateFormatter  
module  
and you could tell it to format all dates of a model a particular way.

Again the syntax is not correct at the moment but something like this  
inside  
a view or in the views helper.

\<% MyModel.include DateFormatter do %\>  
\<% date\_fields :all, “%d %m %y” %\>  
\<% end %\>

I’m not sure how any of the issues that you raised are a problem. Not  
saying they’re not… Just I don’t understand how they are yet.

---

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**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\
**Post date:** [October 26, 2006, 2:37pm UTC](https://www.ruby-forum.com/t/mvc-and-modules-views-telling-models-to-behave/72966/8 "2006-10-26T14:37:54Z")

</div>

On 10/26/06, removed\_email\_address@domain.invalid [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> It seem that what you are after is some kind of presenter object. Take  
> a look at this article:
> 
> [Jay Fields' Thoughts: Rails Model View Controller + Presenter?](http://jayfields.blogspot.com/2006/09/rails-model-view-controller-presenter.html)

Thanx for the link… It was interesting.