# Use of Models - The Very Basics

**URL:** <https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723>\
**Category:** Rails\
**Created:** [June 7, 2009, 8:29pm UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723 "2009-06-07T20:29:38Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![djames](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7ab992/32.png) [@djames](https://www.ruby-forum.com/u/djames)\
**Post date:** [June 7, 2009, 8:29pm UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723/1 "2009-06-07T20:29:38Z")

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Embarrassingly, I must admit that I have never understood models. I  
am hoping that with this post I can clear up a basic question that  
will allow me to get a toe-hold into understanding models. The basic  
question is this:

Do we only use models with databases or do they have other uses?

Models descend from ActiveRecord::Base. That certainly gives rise to  
a notion that models are used exclusively with databases. However, I  
have read plenty of chatter encouraging me to move code out of the  
controller and into the model.

At the moment, I happen to be dealing with a perfect example. In a  
user’s profile I store an integer named ‘flags’. The integer is a  
decimal representation of a set of binary flags that correspond to  
various yes/no configuration selections that the user has made. I  
have written a very short method that will accept 2 arguments, a  
user’s flags integer and the weight of a specific flag. The method  
returns true or false depending on whether the specific flag is set in  
the given flags integer. The method has absolutely nothing to do with  
a database. The question is: Where do I put this method? From the  
description that I have given I think that it is clear that this  
method is back-room, heavy-duty, number-crunching stuff (to use terms  
that I have seen in my reading). So, does it go in the model? If so,  
how do I access it from other places?

Thanks very much for any input.

```
      ... doug
```

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**Author:** ![djames](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7ab992/32.png) [@djames](https://www.ruby-forum.com/u/djames)\
**Post date:** [June 7, 2009, 8:59pm UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723/2 "2009-06-07T20:59:30Z")

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I’m not a Rails pro, but I would like to make the following comments:  
A model

- represents your Data you deal with, like students/products… which  
you  
save in a database!
- should include operations/methods which exclusively deal with the  
object/data, like setter/getter moethds and/or computing specific  
things  
like an access/activation code

The convention is, as far as I now, to keep the controller clean and  
light.  
But in certain scenarios it make sense to keep some functionality in the  
controller. However in you case I would definitely put it into the  
model.  
“The method has absolutely nothing to do with a database”, sure but it  
has a  
lot to do with the data/objects you store there. You call that special  
method on a specific object as I understand you point. You can do  
something  
like  
user.your\_method or user.your\_method(variavble1,variable2) where you  
define  
your\_method in the model file in rails.

Cheers & good luck,

Chris

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<div class="post-metadata">

**Author:** ![djames](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7ab992/32.png) [@djames](https://www.ruby-forum.com/u/djames)\
**Post date:** [June 7, 2009, 11:50pm UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723/3 "2009-06-07T23:50:07Z")

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On Jun 7, 2009, at 2:28 PM, doug wrote:

> Embarrassingly, I must admit that I have never understood models. I  
> am hoping that with this post I can clear up a basic question that  
> will allow me to get a toe-hold into understanding models. The basic  
> question is this:
> 
> Do we only use models with databases or do they have other uses?

Models let you encapsulate business logic.

> Models descend from ActiveRecord::Base. That certainly gives rise to  
> a notion that models are used exclusively with databases. However, I  
> have read plenty of chatter encouraging me to move code out of the  
> controller and into the model.

Not always. For example, I have a project with a SearchResult model;  
it doesn’t correspond directly to a table, but it does leverage  
several other models (7, I think) that do persist data in the database.

> method is back-room, heavy-duty, number-crunching stuff (to use terms  
> that I have seen in my reading). So, does it go in the model? If so,  
> how do I access it from other places?
> 
> Thanks very much for any input.
> 
> ```
> ... doug
> 
> ```

So you’re modeling a set of boolean flags, huh? Do you know about the  
Integer#[] method?

irb\> 3.downto(0) {|i| puts “10[#{i}]==#{10[i]}”}  
10[3]==1  
10[2]==0  
10[1]==1  
10[0]==0  
=\> 3  
irb\> 10.to\_s(2)  
=\> “1010”

The point is that this method has everything to do with the _data_. It  
is probably true that the data is persisted in the database, but this  
method would make sense even if you kept the data in an Array, yes?

Put the method into the User model. Since you didn’t give enough  
specifics, I’ll base an example on somewhat of a tangent since you  
mentioned “back-room”.

class User  
def liberal?  
self.flags[0].nonzero?  
end  
def moderate?  
self.flags[1].nonzero?  
end  
def conservative?  
self.flags[2].nonzero?  
end  
end

Instead of asking political\_leaning(doug.flags, User::Moderate) you  
can just say doug.moderate? and be done. You could define constants  
for the bit/flag numbers, too.

If this doesn’t help you see how to use a model, post some code and  
you might get a different style of answer.

-Rob

Rob B. [http://agileconsultingllc.com](http://agileconsultingllc.com)  
removed\_email\_address@domain.invalid

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<div class="post-metadata">

**Author:** ![djames](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7ab992/32.png) [@djames](https://www.ruby-forum.com/u/djames)\
**Post date:** [June 8, 2009, 2:27am UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723/4 "2009-06-08T02:27:36Z")

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Doug J. wrote:  
[…]

> Do we only use models with databases or do they have other uses?

They certainly have other uses. Models represent any domain object that  
you need. Sometimes these objects will correspond to DB records,  
sometimes not.

> Models descend from ActiveRecord::Base. That certainly gives rise to  
> a notion that models are used exclusively with databases.  
> […]

The Rails community often gives the impression that models have to  
descend from ActiveRecord::Base, but that’s only true _if you need  
ActiveRecord features_. True, most models in Rails apps tend to inherit  
from AR. However, if you’re modeling something that doesn’t interact  
with the DB, there’s generally no need to inherit from AR, but the class  
is still a model because it represents a domain object.  
In other words, whether a class is considered a model has to do with the  
_conceptual_ niche that it fills within the app, not with whether it  
inherits from AR.

Does that help?

## Best,

Marnen Laibow-Koser  
[http://www.marnen.org](http://www.marnen.org)  
removed\_email\_address@domain.invalid

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<div class="post-metadata">

**Author:** ![djames](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7ab992/32.png) [@djames](https://www.ruby-forum.com/u/djames)\
**Post date:** [June 9, 2009, 2:45am UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723/5 "2009-06-09T02:45:07Z")

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Imagine a small vendor needing to process credit card information but  
not wanting, in any cases, to store the data locally. Ideal case for  
ActiveRecord methods without a database persistance.

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**Author:** ![djames](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/7ab992/32.png) [@djames](https://www.ruby-forum.com/u/djames)\
**Post date:** [June 8, 2009, 6:47pm UTC](https://www.ruby-forum.com/t/use-of-models-the-very-basics/169723/6 "2009-06-08T18:47:39Z")

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> Does that help?

Yes, it does. So, I think that you are saying that, in the right  
circumstances, it’s perfectly fine to create a model that inherits  
directly from object. That does help.

FWIW, I’m still digesting Rob’s response. I think that there is  
likely a lot of help there as well. I just need to sort it all out.

Thanks for the input.

```
     ... doug
```