Rails - Apr 2006 - Is eval the only way?

Hi,

I''m trying to write some methods which use a parameter to represent a  
Class name.

A very simplistic example:

def foo(class_name, conditions)
   x = class_name.find(:all, :conditions => "#{conditions}")
end

Unfortunately, this does not work. The only way around this problem  
that I can think of is to use eval:

def foo(class_name, conditions)
   x = eval "#{class_name}.find(:all, :conditions => \"# 
{conditions}''\")"
end

There''s got to be a better way. -- Please help!

: )

Jason

On Wed, Apr 05, 2006 at 05:39:35PM -0400, Jason Tuttle wrote:
} I''m trying to write some methods which use a parameter to represent a
} Class name.
} 
} A very simplistic example:
} 
} def foo(class_name, conditions)
}   x = class_name.find(:all, :conditions => "#{conditions}")
} end
} 
} Unfortunately, this does not work. The only way around this problem  
} that I can think of is to use eval:
[...]
} There''s got to be a better way. -- Please help!

def foo(class_name, conditions)
  x = Kernel.const_get(class_name).find(:all, :conditions =>
"#{conditions}")
end

} : )
} Jason
--Greg

On Apr 05, 2006, at 10:39 pm, Jason Tuttle wrote:
> Hi,
>
> I''m trying to write some methods which use a parameter to
represent
> a Class name.
>
> A very simplistic example:
>
> def foo(class_name, conditions)
>   x = class_name.find(:all, :conditions => "#{conditions}")
> end
>
> Unfortunately, this does not work. The only way around this problem  
> that I can think of is to use eval:
>
> def foo(class_name, conditions)
>   x = eval "#{class_name}.find(:all, :conditions => \"# 
> {conditions}''\")"
> end
>
> There''s got to be a better way. -- Please help!
>
> : )
>
> Jason
Jason

Try this:

   def foo(class_name, conditions)
     ObjectSpace.each_object(Class) do |c|
       return c.find(:all, :conditions => conditions) if c.name ==  
class_name
     end
   end

You''d have to benchmark it to see which performs better, but it looks  
more "Ruby-like" like that.

Ashley

On Apr 05, 2006, at 11:23 pm, Gregory Seidman wrote:
> def foo(class_name, conditions)
>   x = Kernel.const_get(class_name).find(:all, :conditions => "# 
> {conditions}")
> end

Meh... that beats mine :P

Ashley

On 4/5/06, Jason Tuttle <jason@gothamcitymacs.com>
wrote:
> Hi,
>
> I''m trying to write some methods which use a parameter to
represent a
> Class name.
>
> A very simplistic example:
>
> def foo(class_name, conditions)
>    x = class_name.find(:all, :conditions => "#{conditions}")
> end
>
> Unfortunately, this does not work. The only way around this problem
> that I can think of is to use eval:
>
> def foo(class_name, conditions)
>    x = eval "#{class_name}.find(:all, :conditions => \"#
> {conditions}''\")"
> end
>
> There''s got to be a better way. -- Please help!
>
Inside Rails, you can do:
x = class_name.constantize.find(:all, :conditions =>
"#{conditions}")

constantize is a more-readable shortcut for the const_get business.

Thanks Greg!

This works perfectly when run from the console, but generates the  
following error when running in my rails testing environment:

NameError (uninitialized constant Kernel::Rate)

Any thoughts? -- "Rate" is the class name I''m passing to the
method.

: )

Jason

Gregory Seidman <gsslist+ror@...> writes:

 >
 > On Wed, Apr 05, 2006 at 05:39:35PM -0400, Jason Tuttle wrote:
 > } I''m trying to write some methods which use a parameter to  
represent a
 > } Class name.
 > }
 > } A very simplistic example:
 > }
 > } def foo(class_name, conditions)
 > }   x = class_name.find(:all, :conditions => "#{conditions}")
 > } end
 > }
 > } Unfortunately, this does not work. The only way around this problem
 > } that I can think of is to use eval:
 > [...]
 > } There''s got to be a better way. -- Please help!
 >
 > def foo(class_name, conditions)
 >   x = Kernel.const_get(class_name).find(:all, :conditions => "# 
{conditions}")
 > end
 >
 > } : )
 > } Jason
 > --Greg
 >

>> Hi,
>>
>> I''m trying to write some methods which use a parameter to
represent a
>> Class name.
>>
>> A very simplistic example:
>>
>> def foo(class_name, conditions)
>>    x = class_name.find(:all, :conditions =>
"#{conditions}")
>> end
>>
>> Unfortunately, this does not work. The only way around this problem
>> that I can think of is to use eval:
>>
>> def foo(class_name, conditions)
>>    x = eval "#{class_name}.find(:all, :conditions => \"#
>> {conditions}''\")"
>> end
>>
>> There''s got to be a better way. -- Please help!
>>
>>
>
> Inside Rails, you can do:
> x = class_name.constantize.find(:all, :conditions =>
"#{conditions}")
>
> constantize is a more-readable shortcut for the const_get business.
Thanks Wilson! -- That works like a charm.

: )

Jason

>> def foo(class_name, conditions)
>>   x = Kernel.const_get(class_name).find(:all, :conditions => "#
ive been using Object''s const_get instead of Kernel''s. is
there a
difference? and why is there an object and a kernel if not?

-- 
Posted via http://www.ruby-forum.com/.

On Thu, Apr 06, 2006 at 02:08:21AM +0200, carmen wrote:
} 
} >> def foo(class_name, conditions)
} >>   x = Kernel.const_get(class_name).find(:all, :conditions =>
"#
} 
} ive been using Object''s const_get instead of Kernel''s. is
there a
} difference? and why is there an object and a kernel if not?

No, there isn''t:

irb(main):001:0> Object.included_modules
=> [Kernel]
irb(main):002:0>

--Greg

On Wed, Apr 05, 2006 at 06:55:08PM -0400, Jason Tuttle wrote:
} Thanks Greg!
} 
} This works perfectly when run from the console, but generates the  
} following error when running in my rails testing environment:
} 
} NameError (uninitialized constant Kernel::Rate)
} 
} Any thoughts? -- "Rate" is the class name I''m passing to
the method.

Try this, then:

def foo(class_name, conditions)
  x = Kernel.const_get("::#{class_name}").find(:all,
      :conditions => "#{conditions}")
end

} : )
} Jason
--Greg