# Named\_scopes

**URL:** <https://www.ruby-forum.com/t/named-scopes/171006>\
**Category:** Rails\
**Created:** [June 25, 2009, 9:14am UTC](https://www.ruby-forum.com/t/named-scopes/171006 "2009-06-25T09:14:07Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![talex83](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/54ee81/32.png) [@talex83](https://www.ruby-forum.com/u/talex83)\
**Post date:** [June 25, 2009, 9:14am UTC](https://www.ruby-forum.com/t/named-scopes/171006/1 "2009-06-25T09:14:07Z")

</div>

Hey all,

I’m learning rails and am trying to put together a generic ACL check  
for all models. I’ve been able to sucessfully implement it as a  
method for all models by decorating ActiveRecord::Base. But when I  
try to do the “rails way” of creating an association (and thereby  
taking advantage of the ORM), I don’t get very far…

Here is the code:

class ActiveRecord::Base

has\_many(:permissions)  
named\_scope(:acl\_check, lambda do |user\_id, method|  
{  
:include =\> :permission,  
:conditions =\> [  
[“permissions.user\_id=?”, user\_id],  
[“permissions.method=?”, method],  
[“permissions.classname=?”, self.class.name]  
]  
}  
end)

# Conducts a permission check for the entire class.

def self.check\_acl(user\_id, method)

```
# Perform the permission check by User.
permission_check =

```

Permission.find\_by\_user\_id\_and\_instance\_id\_and\_classname\_and\_method  
(user\_id, nil, self.class.name, method)  
if(permission\_check)  
# If the row exists, we generate a hit.  
return(true)  
end

```
# Perform the permission check by Role.

# Otherwise, the permissions check was a miss.
return(false)

```

end

# Conducts a permission check for the current instance.

def check\_acl?(user\_id, method)

```
# Perform the permission check by User.
permission_check =

```

Permission.find\_by\_user\_id\_and\_instance\_id\_and\_classname\_and\_method  
(user\_id, self.id, self.class.name, method)  
if(permission\_check)  
# If the row exists, we generate a hit.  
return(true)  
end

```
# Perform the permission check by Role.

# Otherwise, the permissions check was a miss.
return(false)

```

end

end

Currently, calling check\_acl on either an instance of a model or the  
model class itself functions as expected. But attempting to call  
acl\_check (my named\_scope), just results in a method not found.

At the very least I’d like to know why this isn’t working and if at  
all possible, I’d like to hear some ideas on how I can make this  
work. I’ve heard about using modules, but I’d like to not have to  
include a source file in each model. Ideally doing it the object-  
oriented way would make me happier 🙂

But again, I’d love to hear details on why ActiveRecord isn’t making  
this happen…

---

<div class="post-metadata">

**Author:** ![talex83](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/54ee81/32.png) [@talex83](https://www.ruby-forum.com/u/talex83)\
**Post date:** [June 25, 2009, 10:56am UTC](https://www.ruby-forum.com/t/named-scopes/171006/2 "2009-06-25T10:56:39Z")

</div>

On Jun 25, 1:07 am, Omega [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Currently, calling check\_acl on either an instance of a model or the  
> model class itself functions as expected. But attempting to call  
> acl\_check (my named\_scope), just results in a method not found.

So you’re trying to call a named scope on an instance of your model ?  
That won’t work because named scopes aren’t supposed to work that way.  
In a nutshell scopes are about narrowing down the results of a find  
(although they are also handy for adding other options to a find), eg  
Person.active scopes the find to those people with active=true. When  
you are just talking about a single object you have already loaded,  
scopes don’t make a lot of sense.

A fairly standard way of doing this would be to add a class method to  
ActiveRecord::Base (eg acts\_as\_permissioned) and then calling that  
method would add required associations and so on, so a model which  
does use this stuff looks like

class Something \< AR::Base  
acts\_as\_permissioned  
end

(which at the end of the day is using modules and what not, but I find  
this a whole lot clearer than having stuff inserted into the base  
class. at least hear you have a clear statement at the top that this  
class is using the permissions stuff)

Fred

(ps you probably don’t want self.class.name in your self.check\_acl  
method, since this will always evaluate to ‘Class’ )