# How to pass a variable from a model method to a controller

**URL:** <https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453>\
**Category:** Rails\
**Created:** [April 25, 2009, 12:30pm UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453 "2009-04-25T12:30:56Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![tharrisx](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tharrisx](https://www.ruby-forum.com/u/tharrisx)\
**Post date:** [April 25, 2009, 12:30pm UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453/1 "2009-04-25T12:30:56Z")

</div>

Hi there,

how can I pass a variable from a model method to the controller that  
calls this method?

In the below code, I tried by placing “return @errormessage” in the  
model method and then trying to retrieve it in the controller, but it’s  
wrong. What’s the correct way to do that?

Here’s what it looks like until now (simplified)…

# In my controller:

def whatever  
if @user.does\_my\_check\_pass? # \<= calls the model method  
below…  
[…]  
else  
flash.now[:error] = @errormessage # \<= the variable from the  
method  
render :update do |page|  
page.replace\_html ‘flash\_messages’, flash\_messages  
end  
end  
end

# In my model:

def does\_my\_check\_pass?  
if […some conditions…]  
return true  
else  
return @errormessage = “There was an error.” # \<= the variable  
return false  
end  
end

Thanks a lot for your help!  
Tom

---

<div class="post-metadata">

**Author:** ![tharrisx](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tharrisx](https://www.ruby-forum.com/u/tharrisx)\
**Post date:** [April 25, 2009, 3:32pm UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453/2 "2009-04-25T15:32:20Z")

</div>

Tom Ha wrote:

> Hi there,
> 
> how can I pass a variable from a model method to the controller that  
> calls this method?
> 
> In the below code, I tried by placing “return @errormessage” in the  
> model method and then trying to retrieve it in the controller, but it’s  
> wrong. What’s the correct way to do that?
> 
> Here’s what it looks like until now (simplified)…
> 
> # In my controller:
> 
> def whatever  
> if @user.does\_my\_check\_pass? # \<= calls the model method  
> below…  
> […]  
> else  
> flash.now[:error] = @errormessage # \<= the variable from the  
> method  
> render :update do |page|  
> page.replace\_html ‘flash\_messages’, flash\_messages  
> end  
> end  
> end
> 
> # In my model:
> 
> def does\_my\_check\_pass?  
> if […some conditions…]  
> return true  
> else  
> return @errormessage = “There was an error.” # \<= the variable  
> return false  
> end  
> end
> 
> Thanks a lot for your help!  
> Tom

How about

> # In my model:
> 
> def does\_my\_check\_pass?  
> if […some conditions…]  
> return true  
> else  
> return “There was an error.”  
> end  
> end

> # In my controller:
> 
> def whatever  
> if (result = @user.does\_my\_check\_pass) == true  
> […]  
> else  
> flash.now[:error] = result

1. Note that both a string and true _evaluate to true_ in an if  
statement, so you couldn’t write:

if (result = @user.does\_my\_check\_pass)  
…

The condition would always evaluate to true.

1. Experienced ruby programmers would not write “return”:

> # In my model:
> 
> def does\_my\_check\_pass?  
> if […some conditions…]  
> true  
> else  
> “There was an error.”  
> end  
> end

---

<div class="post-metadata">

**Author:** ![tharrisx](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tharrisx](https://www.ruby-forum.com/u/tharrisx)\
**Post date:** [April 25, 2009, 5:26pm UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453/3 "2009-04-25T17:26:17Z")

</div>

You got that right, I’m not (yet) an experienced ruby programmer, but  
you’ve just helped me to get a step further - so thanks a lot, bro !

---

<div class="post-metadata">

**Author:** ![tharrisx](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tharrisx](https://www.ruby-forum.com/u/tharrisx)\
**Post date:** [April 27, 2009, 9:23am UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453/4 "2009-04-27T09:23:42Z")

</div>

Thanks! Always good to get some critical remarks & advice…

---

<div class="post-metadata">

**Author:** ![tharrisx](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tharrisx](https://www.ruby-forum.com/u/tharrisx)\
**Post date:** [April 27, 2009, 8:49am UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453/5 "2009-04-27T08:49:52Z")

</div>

Not 100% sure I understand what you’re trying to do, but here are a  
couple  
of items that strike me based on the code posted.

First, your model method has two return statements. I don’t know  
whether  
Ruby will throw up some kind of parsing error to that, but certainly the  
second of those will never be executed.

Second, putting error message text in the model is probably not what you  
want to be doing. Your error messages are not part of your business  
logic.  
Most people put these things in the controller, although strictly  
speaking,  
they probably belong in the view (though Rails doesn’t make it very easy  
to  
put them there and keep your code looking good).

Finally, I assume your controller is taking in some input as HTTP  
request  
params before it runs this “does\_my\_check\_pass?” method. If so, then I  
guess your check should actually be a part of the standard ActiveRecord  
validation process. In that case, inputs will be checked every time you  
create or update a new User object rather than in any case you remember  
to  
call it. The proper flow control through the controller action should  
be  
pretty standard: rececive inputs, delegate validation to the model,  
perform  
necessary model operations (CRUD), and render/redirect user output.

Hope that is helpful to you.

On Sat, Apr 25, 2009 at 12:30 PM, Tom Ha

---

<div class="post-metadata">

**Author:** ![tharrisx](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/e19adc/32.png) [@tharrisx](https://www.ruby-forum.com/u/tharrisx)\
**Post date:** [April 27, 2009, 10:34am UTC](https://www.ruby-forum.com/t/how-to-pass-a-variable-from-a-model-method-to-a-controller/166453/6 "2009-04-27T10:34:56Z")

</div>

Chris K. wrote:

> Second, putting error message text in the model is probably not what you  
> want to be doing. Your error messages are not part of your business  
> logic.  
> Most people put these things in the controller, although strictly  
> speaking,  
> they probably belong in the view (though Rails doesn’t make it very easy  
> to  
> put them there and keep your code looking good).

I’m reading AWDWR(3rd.) and in the first full example, which is a  
shopping cart, there is a user interface with CRUD operations for  
entering new Product’s in the database. The example uses method calls  
to standard rails validation methods in the model, for example:

```
validates_presence_of :description

```

as well as a custom validation method:

```
  validate :price_must_be_at_least_a_cent

protected
  def price_must_be_at_least_a_cent
    if price.nil? || price < .01
      errors.add(:price, 'should be at least .01')
    end
  end

```

That has an error message in the model, which seems contrary to your  
advice. Also, at the start of the section on validation, the authors  
say:

* * *

## So, where to put the validation? The model layer is the gatekeeper between the world of code and the database. Nothing to do with our application comes out of the database or gets stored in the database that doesn’t first go through the model. This makes models an ideal place to put validation;…

If you have several controllers all accessing the database through the  
same model, then wouldn’t you “get wet” duplicating the validation in  
each controller?