# Rails namespace help requested

**URL:** <https://www.ruby-forum.com/t/rails-namespace-help-requested/53430>\
**Category:** Rails\
**Created:** [December 14, 2005, 3:33pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430 "2005-12-14T15:33:12Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![magic6435](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/57b2e6/32.png) [@magic6435](https://www.ruby-forum.com/u/magic6435)\
**Post date:** [December 14, 2005, 3:33pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430/1 "2005-12-14T15:33:12Z")

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Hi all -

I posted yesterday with the subject “namespace pollution” and with the  
high traffic on this list, it’s kind of disappeared and I’m in need of  
a quick answer so i can move on. To recap quickly, can someone tell  
if Rails is somehow forcing all modules into a single namespace? I  
have a model class StateProvince and inside a webservice module in my  
lib/ directory I have a StateProvince as well but no matter what I do  
when running under Rails I get a superclass mismatch error. This  
doesn’t happen when I have standalone ruby code in similar situations.

Thanks for any help  
Mike

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**Author:** ![magic6435](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/57b2e6/32.png) [@magic6435](https://www.ruby-forum.com/u/magic6435)\
**Post date:** [December 14, 2005, 4:09pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430/2 "2005-12-14T16:09:25Z")

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zdennis wrote:

> Michael E. wrote:

> class B; end  
> class B \< A; end # error!!
> 
> This is the scenario you’re hitting with your namespace clash. Your  
> StateProvince class is being initalized, then when it gets around to  
> loading your StateProvince module it seems you’re trying to define  
> inheritance, and you can’t do that now.

I don’t mean to say it’s anything you’re doing on purpose. I think ruby  
finds your StateProvince  
class definition first, then it finds the StateProvince model  
definition, which is where it tries to  
subclass ActiveRecord::Base. At this point Ruby already has a definition  
for StateProvince, and  
although ruby lets us reopen the class we can’t subclass it because Ruby  
defines the superclass of a  
class when the class is first read in.

Zach

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**Author:** ![magic6435](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/57b2e6/32.png) [@magic6435](https://www.ruby-forum.com/u/magic6435)\
**Post date:** [December 14, 2005, 4:00pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430/3 "2005-12-14T16:00:20Z")

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Michael E. wrote:

> 

By default Rails classes are using toplevel namespace; ie: ActiveRecord,  
ActionController,  
ActionView, etc…

Rails also does not put your models into a separate namespace (though i  
wish it would =), and those  
also are toplevel. ie: User, Account, Session, Group, Article.

If you have any classes that you wrote that have the same names as your  
models or other toplevel  
classes/modules that Rails is using you need to either a) rename them or  
b) move them inside of  
another namespace.

The problem you are having is that the first time you define/open a  
class it has to define it’s  
superclass.

class A ; end  
class B \< A; end

You cannot define/open a class and then later try to subclass it, ie:

class A; end  
class B; end  
class B \< A; end # error!!

This is the scenario you’re hitting with your namespace clash. Your  
StateProvince class is being  
initalized, then when it gets around to loading your StateProvince  
module it seems you’re trying to  
define inheritance, and you can’t do that now.

If you have namespace clashes but you are in your namespace you can use  
:: syntax to ensure you get  
the toplevel class/module. For example:

class StateProvince  
end

module MyNameSpace  
class StateProvince  
end

```
module MoreModules
   class MyStateProvinceModel < StateProvince
   end
end

```

end

In the above code code your MyStateProvinceModel is going to subclass  
MyNameSpace::StateProvince  
because that is the first constant ruby finds while it is looking for  
“StateProvince”. This may be  
wrong because your MyStateProvinceModel might need to subclass the  
toplevel StateProvince class.  
This is where the “::” comes in handy:

class StateProvince  
end

module MyNameSpace  
class StateProvince  
end

```
module MoreModules
   class MyStateProvinceModel < ::StateProvince
   end
end

```

end

The leading :: on any constant will force ruby to look at the most  
toplevel constant.

I hope this helps more then it confuses,

Zach

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**Author:** ![magic6435](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/57b2e6/32.png) [@magic6435](https://www.ruby-forum.com/u/magic6435)\
**Post date:** [December 14, 2005, 6:12pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430/4 "2005-12-14T18:12:48Z")

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Michael E. wrote:

> class StateProvince  
> end  
> end
> 
> Isn’t the namespace declared for the class inside the module as  
> ::WebServiceModule::StateProvince and the Rails model as  
> ::StateProvince? Aren’t those different objects in the eyes or Ruby?

Yes.

> Also I’m not doing inheritance in my WebServiceModule, I’m just  
> declaring a namespace right?

In your WebServiceModule you aren’t doing any explicit inheritance. From  
your post from yesterday:

```
but when I run my code in Rails, I get a superclass mismatch error
when I include the module.

```

If you include you WebServiceModule in your top level, it will have a  
problem when it finds the  
StateProvince model. By saying:

```
include WebServiceModule

```

It will move WebServiceModule::StateProvince (and all other constants)  
to scope that your “include”  
statement is in. In this case it is in the toplevel/global scope and it  
will be accessible as  
::StateProvince.

So now that it is toplevel accessible and ruby finds your StateService  
model which tries to subclass  
ActiveRecord::Base you get your superclass problem!

I hope this helps!

> I’m a bit new to Ruby so it’s possible I’m mixing this up but this is  
> what I understood from reading the pickaxe book.

ooh, good book. =)

Zach

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**Author:** ![magic6435](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/57b2e6/32.png) [@magic6435](https://www.ruby-forum.com/u/magic6435)\
**Post date:** [December 14, 2005, 5:03pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430/5 "2005-12-14T17:03:35Z")

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HI Zach -

THanks very much for your help. I’m not sure I understand why my  
clash exists though because I have this exact scenario:

class StateProvince \< ActiveRecord::Base  
end

# this is in a directory of lib/ws

module WebServiceModule  
class StateProvince  
end  
end

Isn’t the namespace declared for the class inside the module as  
::WebServiceModule::StateProvince and the Rails model as  
::StateProvince? Aren’t those different objects in the eyes or Ruby?

Also I’m not doing inheritance in my WebServiceModule, I’m just  
declaring a namespace right?

I’m a bit new to Ruby so it’s possible I’m mixing this up but this is  
what I understood from reading the pickaxe book.

Thanks again for your help.

MIke

---

<div class="post-metadata">

**Author:** ![magic6435](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/57b2e6/32.png) [@magic6435](https://www.ruby-forum.com/u/magic6435)\
**Post date:** [December 14, 2005, 9:49pm UTC](https://www.ruby-forum.com/t/rails-namespace-help-requested/53430/6 "2005-12-14T21:49:51Z")

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AH!!! Thank you!!! I guess I needed to get whacked with a 2x4  
regarding mixing in a module…The pickaxe booking didn’t explain it  
as concisely. Thanks again

Mike