# Where to put constants

**URL:** <https://www.ruby-forum.com/t/where-to-put-constants/126388>\
**Category:** Rails\
**Created:** [January 17, 2008, 10:13pm UTC](https://www.ruby-forum.com/t/where-to-put-constants/126388 "2008-01-17T22:13:01Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Pito](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e68b1a/32.png) [@Pito](https://www.ruby-forum.com/u/Pito)\
**Post date:** [January 17, 2008, 10:13pm UTC](https://www.ruby-forum.com/t/where-to-put-constants/126388/1 "2008-01-17T22:13:01Z")

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I have a column in my database which is a code, kind of a record  
type.

For example, in model Vehicle, I use a 1 for CAR and a 2 for BOAT in  
the database.

I want to have constants accessible so that the mapping to 1 and 2 is  
in only one place.

So I created constants:

CAR = 1  
BOAT = 2

Question is, where to put these.

If I put then in the Vehicle model then they are available only there  
and I need them elsewhere, if no-where else, then in my rspec tests.

But also, I use them in the interface of other classes, for example I  
might have a Dealer model which has\_many :vehicles. And I might want  
to have a find\_all(vehicle\_type) method on Dealer which now needs  
those constants too.

So now I have them in config/initializers but I am not sure that this  
is an appropriate use of that. After all in a way CAR and BOAT are  
parts of the Vehicle model and should live only there. On the other  
hand they are also part of the public interface and are used elsewhere  
too.

Just a question of best practice. Any commetns?

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**Author:** ![Pito](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e68b1a/32.png) [@Pito](https://www.ruby-forum.com/u/Pito)\
**Post date:** [January 17, 2008, 10:21pm UTC](https://www.ruby-forum.com/t/where-to-put-constants/126388/2 "2008-01-17T22:21:16Z")

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Pito wrote:

> Just a question of best practice. Any commetns?

you can put them in your config/environment.rb file

VEHICULAR\_TYPES = {:CAR =\> 1, :BOAT =\> 2} # non-oo type specifications  
to support db operations

or you can stick them in any appropriate model above the class  
definition

hth

ilan

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**Author:** ![Pito](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e68b1a/32.png) [@Pito](https://www.ruby-forum.com/u/Pito)\
**Post date:** [January 17, 2008, 11:52pm UTC](https://www.ruby-forum.com/t/where-to-put-constants/126388/3 "2008-01-17T23:52:38Z")

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On 17 Jan 2008, at 21:12, Pito wrote:

> So I created constants:
> 
> CAR = 1  
> BOAT = 2
> 
> Question is, where to put these.
> 
> If I put then in the Vehicle model then they are available only there  
> and I need them elsewhere, if no-where else, then in my rspec tests.

They will be available elsewhere, you just need to say Vehicle::CAR

Fred

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**Author:** ![Pito](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e68b1a/32.png) [@Pito](https://www.ruby-forum.com/u/Pito)\
**Post date:** [January 18, 2008, 12:04am UTC](https://www.ruby-forum.com/t/where-to-put-constants/126388/4 "2008-01-18T00:04:28Z")

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Is there really a need to store the number on the field; Are you  
supporting  
a legacy system as well as a new system?

If not, why not just store “car” or “boat” on the field. Even better  
would  
be to have a vehicle types table. When you want to add more vehicle  
types  
then you’ll have to update this table and not the constant.

On Jan 18, 2008 7:51 AM, Ilan B. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> >

–  
Ryan B.

> **[frozenplague.net](http://www.frozenplague.net)**
>
> This domain may be for sale!

Feel free to add me to MSN and/or GTalk as this email.

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**Author:** ![Pito](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/e68b1a/32.png) [@Pito](https://www.ruby-forum.com/u/Pito)\
**Post date:** [January 18, 2008, 7:14pm UTC](https://www.ruby-forum.com/t/where-to-put-constants/126388/5 "2008-01-18T19:14:46Z")

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Yet another solution is to use inheritance. This would work best with  
a limited number of types. I’m not necessarily advocating this  
approach, but I would say two things:

1. This approach would let Rails take care of guaranteeing that your  
model constants match your database constants.

2. It actually would be object-oriented at the same time, since a Car  
is-a Vehicle.

I’m just saying…

///ark