# Implementing a credit-based system

**URL:** <https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721>\
**Category:** Rails\
**Created:** [August 1, 2008, 2:46pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721 "2008-08-01T14:46:14Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 2:46pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/1 "2008-08-01T14:46:14Z")

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Hey all, fairly new to Rails here and I am currently building my first  
Rails app.

I am building an app that will require users to purchase credits in  
order to post items on the site. These credits will be purchased in  
blocks of credits like 5, 10, 20, etc. (similar to [istockphoto.com](http://istockphoto.com)).

Here is how I picture setting up the credits in my app.

Credits Model - This model would determine the different credit  
packages (5,10,20) along with the price of each credit package.

This model would “belong to” User and the User “has many” Credits,  
right?

I then assume that the controller for my credits is where I would  
handle the logic of adding credits to the user accounts, making sure  
the credit is deducted when they list an item, and keeping track of  
how many credits a user has at any given time. I also assume that as  
credits are purchased, and the user needs to be emailed notification  
of that purchase, that logic would also live in this same controller,  
right?

Am I on the right track here as far as mapping out what goes where? I  
am really loving Rails so far, I am just having a bit of a hard time  
wrapping my head around where logic goes and what handles what and how  
they all tie in together!

I appreciate any help or feedback that you guys can give me! Thanks!

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**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 2:56pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/2 "2008-08-01T14:56:47Z")

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On 1 Aug 2008, at 13:45, CPerry wrote:

> Credits Model - This model would determine the different credit  
> packages (5,10,20) along with the price of each credit package.
> 
> This model would “belong to” User and the User “has many” Credits,  
> right?

Part of this depends on your requirements, but you could easily have 2  
models:  
Credit (belongs\_to user, and user has many credits). 1 for each one  
purchased and tracks stuff like if it should expire, what it was used  
for, etc…

Another model which handles whatever packages people can purchase.

> I then assume that the controller for my credits is where I would  
> handle the logic of adding credits to the user accounts, making sure  
> the credit is deducted when they list an item, and keeping track of  
> how many credits a user has at any given time. I also assume that as  
> credits are purchased, and the user needs to be emailed notification  
> of that purchase, that logic would also live in this same controller,  
> right?

I would have very very little in the controller, probably as simple as

def purchase  
@package = Package.find params[:id]  
current\_user.purchase @package  
end

Similarly, at the point where the user uploads some content, i doubt  
I’d do much more than call a method on the user (and the logic of  
removing credits etc… would live there).

You might want to do some of the emaily stuff via an observer.  
There’s a saying out there which is a good rule of thumb: ‘skinny  
controllers, fat models’

Fred

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**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 3:25pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/3 "2008-08-01T15:25:31Z")

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Frederick, Thanks for the clarification. I see what you are saying  
with making sure there is as little logic as possible in the  
controllers.

I also see what you are saying with having 2 separate controllers (1  
for the credits and 1 for the packages). I had not thought about it  
that way before, but that does seem to make more sense to me.

For some reason, I keep thinking that I have to have as few models and  
controllers as possible, when I think I should be concentrating more  
on building it the way it makes the most sense.

–Cory

On Aug 1, 8:55 am, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 3:51pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/4 "2008-08-01T15:51:59Z")

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Yeah sorry! I meant 2 separate MODELS not controllers! That second cup  
of coffee hasn’t quite kicked in yet.

–Cory

On Aug 1, 9:38 am, Frederick C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 3:39pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/5 "2008-08-01T15:39:36Z")

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On 1 Aug 2008, at 14:24, CPerry wrote:

> Frederick, Thanks for the clarification. I see what you are saying  
> with making sure there is as little logic as possible in the  
> controllers.
> 
> I also see what you are saying with having 2 separate controllers (1  
> for the credits and 1 for the packages). I had not thought about it  
> that way before, but that does seem to make more sense to me.

I’m not even sure if there is a credits controller - you never  
directly interact with them : you buy packages, and then you perform  
uploads or other actions (which as a side effect use a credit).  
The only thing I can think of is a page which showed you how many  
credits you have or other audit traily types of information (but that  
could easily just boil down to some text on the ‘my account’ page).

Fred

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**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 8:52pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/6 "2008-08-01T20:52:30Z")

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On Fri, Aug 1, 2008 at 8:45 AM, CPerry [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Credits Model - This model would determine the different credit  
> packages (5,10,20) along with the price of each credit package.

Is a Credits model necessary? Would it be easier to have a credits  
attribute  
(int) on the User model, and increment/decrement accordingly?

> This model would “belong to” User and the User “has many” Credits,  
> right?
> 
> I then assume that the controller for my credits is where I would  
> handle the logic of adding credits to the user accounts, making sure  
> the credit is deducted when they list an item, and keeping track of  
> how many credits a user has at any given time. I also assume that as  
> credits are purchased, and the user needs to be emailed notification  
> of that purchase, that logic would also live in this same controller,  
> right?

How about a Package model (which would hold the price for the package,  
number of credits, and any other attributes you’d like). Then define a  
method on the User model called “apply\_credits(number)” which takes the  
number of credits to apply as an argument. Then, when they purchase the  
package, do “@user.apply\_credits(@package.num\_credits)” (in the  
controller  
that’s handling the purchase) to increment the credits.

You may want to watch a few Railscasts (  
[Ruby on Rails Screencasts - RailsCasts](http://railscasts.com/episodes/archive)), especially #4 - Move Find into  
Model. It’s a good idea to have fat models and skinny controllers–move  
all  
your complex logic to the model and keep the controller terse.

–  
Tim

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<div class="post-metadata">

**Author:** ![CPerry](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/9d8465/32.png) [@CPerry](https://www.ruby-forum.com/u/CPerry)\
**Post date:** [August 1, 2008, 8:54pm UTC](https://www.ruby-forum.com/t/implementing-a-credit-based-system/144721/7 "2008-08-01T20:54:15Z")

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On 1 Aug 2008, at 19:15, Tim G. wrote:

> Credits Model - This model would determine the different credit  
> packages (5,10,20) along with the price of each credit package.
> 
> Is a Credits model necessary? Would it be easier to have a credits  
> attribute (int) on the User model, and increment/decrement  
> accordingly?

Quite possibly, I think the key point is whether the audit trail is  
important: do you need to know where the credits have come from (for a  
given user), what they spent them on etc… ie do you want to be able  
to track them?

Fred