# Best way to propogate model rules to controller?

**URL:** <https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366>\
**Category:** Rails\
**Created:** [April 10, 2006, 12:29pm UTC](https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366 "2006-04-10T12:29:06Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [April 10, 2006, 12:29pm UTC](https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366/1 "2006-04-10T12:29:06Z")

</div>

Hey everybody,

I’ve got a model that represents kind of a turn-based games. Certain  
actions can only be made unders certain conditions. For simplicity,  
we’ll say that the only condition for a particular action is that the  
weekday be Tuesday.

def add\_vote  
raise ‘You cannot vote today’ unless Date.today.wday == 2  
…  
end

In my controller I want to show a link, but only if the user is  
allowed to vote. I’m wondering the best way to do this. I think the  
best way is to make another method, which I can call from within both  
the model and controller.

def allow\_vote?  
Date.today.wday == 2  
end

def add\_vote  
raise ‘You cannot vote today’ unless Date.today.wday == 2  
…  
end

Then in my view I can just do \<% unless game.allow\_vote? %\> to hide  
the link. In the controller actions that handle voting, I just rescue  
the exception and display an error if necessary.

Does that seem like a good approach, or is there something better? I  
need this as some rules vary from game to game, and are stored in the  
db for each game.

Pat

---

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [April 10, 2006, 1:55pm UTC](https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366/2 "2006-04-10T13:55:45Z")

</div>

On Mon, Apr 10, 2006 at 04:28:29AM -0600, Pat M. wrote:  
} I’ve got a model that represents kind of a turn-based games. Certain  
} actions can only be made unders certain conditions. For simplicity,  
} we’ll say that the only condition for a particular action is that the  
} weekday be Tuesday.  
[…]

This is business logic, and is appropriate for inclusion in your model.

} In my controller I want to show a link, but only if the user is  
} allowed to vote. I’m wondering the best way to do this. I think the  
} best way is to make another method, which I can call from within both  
} the model and controller.  
}  
} def allow\_vote?  
} Date.today.wday == 2  
} end

The above method belongs in your model. If it depended on which user was  
trying to vote, the user should be passed as an argument to the method.

} def add\_vote  
} raise ‘You cannot vote today’ unless Date.today.wday == 2  
} …  
} end

This method should probably be an action in your controller, and it  
should  
almost certainly give a nicer response than an exception. It should also  
be  
implemented more like (pseudocode):

def add\_vote  
#param stuff…  
if @game.allow\_vote?  
@game.votes.create(…)  
render :action =\> ‘voted’  
else  
render :action =\> ‘rejectvote’  
end  
end

} Then in my view I can just do \<% unless game.allow\_vote? %\> to hide  
} the link.

Yes.

} In the controller actions that handle voting, I just rescue the  
exception  
} and display an error if necessary.  
}  
} Does that seem like a good approach, or is there something better? I  
} need this as some rules vary from game to game, and are stored in the  
} db for each game.

There is no need for an exception at all, just a method on your model  
that  
determines whether voting is allowed. If this determination depends on  
data  
in the database, the allow\_vote? method will be somewhat more complex.  
If  
it depends on the game type, meaning it make sense to implement the  
allow\_vote? method separately for each game type, you probably want to  
look  
into Single Table Inheritance (STI) and implement allow\_vote? separately  
in  
each subclass.

} Pat  
–Greg

---

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [April 10, 2006, 2:21pm UTC](https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366/3 "2006-04-10T14:21:02Z")

</div>

Sorry, I wasn’t clear as to where the methods would go 🙂

allow\_vote? and add\_vote would both be in the model. add\_vote would  
throw an exception if the tries to submit a vote when he shouldn’t.  
This shouldn’t even happen, so it’s exceptional.

In my view, I would use the model’s allow\_vote? method to see if I  
should even display a link. In the controller that collects the vote,  
it will just proxy it on to the model’s submit\_vote method, displaying  
an error if an exception is thrown. The only way an exception would  
be thrown is if the user were to directly access the submit\_vote  
action when he wasn’t supposed to (by creating a form of his own or  
something like that).

Does that make more sense? Basically the model itself should know  
when votes are allowed, and the view uses these allow\_xx? helpers to  
determine what links/partials to render.

Pat

---

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [April 10, 2006, 3:23pm UTC](https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366/4 "2006-04-10T15:23:01Z")

</div>

On 4/10/06, Gregory S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

---

<div class="post-metadata">

**Author:** ![pergesu](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/22d042/32.png) [@pergesu](https://www.ruby-forum.com/u/pergesu)\
**Post date:** [April 10, 2006, 3:19pm UTC](https://www.ruby-forum.com/t/best-way-to-propogate-model-rules-to-controller/57366/5 "2006-04-10T15:19:45Z")

</div>

On Mon, Apr 10, 2006 at 06:19:45AM -0600, Pat M. wrote:  
} Sorry, I wasn’t clear as to where the methods would go 🙂  
}  
} allow\_vote? and add\_vote would both be in the model. add\_vote would  
} throw an exception if the tries to submit a vote when he shouldn’t.  
} This shouldn’t even happen, so it’s exceptional.  
}  
} In my view, I would use the model’s allow\_vote? method to see if I  
} should even display a link. In the controller that collects the vote,  
} it will just proxy it on to the model’s submit\_vote method, displaying  
} an error if an exception is thrown. The only way an exception would  
} be thrown is if the user were to directly access the submit\_vote  
} action when he wasn’t supposed to (by creating a form of his own or  
} something like that).

You should check allow\_vote? in the voting controller action rather than  
just calling a method that could throw an exception. And the add\_vote  
method should use the allow\_vote? method in its test so the checking  
code  
is maintained in a single method (DRY principle). Other than that, sure.

} Does that make more sense? Basically the model itself should know  
} when votes are allowed, and the view uses these allow\_xx? helpers to  
} determine what links/partials to render.

The view should use allow\_xx? to conditionally display links/whatever,  
the  
controller should use allow\_xx? to handle malicious/mistaken actions,  
and  
the model should use allow\_xx? to sanity check its mutators. All the  
checking happens in a single method, which means you only have to  
maintain  
it in one place (DRY principle).

} Pat  
–Greg

} On 4/10/06, Gregory S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:  
} \> On Mon, Apr 10, 2006 at 04:28:29AM -0600, Pat M. wrote:  
} \> } I’ve got a model that represents kind of a turn-based games.  
Certain  
} \> } actions can only be made unders certain conditions. For  
simplicity,  
} \> } we’ll say that the only condition for a particular action is that  
the  
} \> } weekday be Tuesday.  
} \> […]  
} \>  
} \> This is business logic, and is appropriate for inclusion in your  
model.  
} \>  
} \> } In my controller I want to show a link, but only if the user is  
} \> } allowed to vote. I’m wondering the best way to do this. I think  
the  
} \> } best way is to make another method, which I can call from within  
both  
} \> } the model and controller.  
} \> }  
} \> } def allow\_vote?  
} \> } Date.today.wday == 2  
} \> } end  
} \>  
} \> The above method belongs in your model. If it depended on which user  
was  
} \> trying to vote, the user should be passed as an argument to the  
method.  
} \>  
} \> } def add\_vote  
} \> } raise ‘You cannot vote today’ unless Date.today.wday == 2  
} \> } …  
} \> } end  
} \>  
} \> This method should probably be an action in your controller, and it  
should  
} \> almost certainly give a nicer response than an exception. It should  
also be  
} \> implemented more like (pseudocode):  
} \>  
} \> def add\_vote  
} \> #param stuff…  
} \> if @game.allow\_vote?  
} \> @game.votes.create(…)  
} \> render :action =\> ‘voted’  
} \> else  
} \> render :action =\> ‘rejectvote’  
} \> end  
} \> end  
} \>  
} \> } Then in my view I can just do \<% unless game.allow\_vote? %\> to  
hide  
} \> } the link.  
} \>  
} \> Yes.  
} \>  
} \> } In the controller actions that handle voting, I just rescue the  
exception  
} \> } and display an error if necessary.  
} \> }  
} \> } Does that seem like a good approach, or is there something better?  
I  
} \> } need this as some rules vary from game to game, and are stored in  
the  
} \> } db for each game.  
} \>  
} \> There is no need for an exception at all, just a method on your  
model that  
} \> determines whether voting is allowed. If this determination depends  
on data  
} \> in the database, the allow\_vote? method will be somewhat more  
complex. If  
} \> it depends on the game type, meaning it make sense to implement the  
} \> allow\_vote? method separately for each game type, you probably want  
to look  
} \> into Single Table Inheritance (STI) and implement allow\_vote?  
separately in  
} \> each subclass.  
} \>  
} \> } Pat  
} \> --Greg  
} \>  
} \> \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
} \> Rails mailing list  
} \> removed\_email\_address@domain.invalid  
} \> [http://lists.rubyonrails.org/mailman/listinfo/rails](http://lists.rubyonrails.org/mailman/listinfo/rails)  
} \>  
}