Rails - Jun 2006 - using a variable as substitute for a method

That probably isn''t the right title for this topic, but I''m
not sure how
else to explain in succintly. I''m sorry if this is obvious but I 
couldn''t find the answer in the Ruby/Rails docs.

How do I use a variable as a substitute for a method/field, so that I 
can call the object with the variable that contains the method name.

For example, say I have the object Product, that has methods Price, 
Last_Price, Average_Price.

I want to be able to return the value of either of those three fields 
based on the user selection. Ie, user selection is stored in 
params[:foo], which I assign to variable field_to_show, and I want to be 
able to call:

Product.field_to_show

which should output Product.Price (if params[:foo] contained
''Price'')

Currently this gives a no method error.

I know that I can do
case params[:foo]
    when "Price"
         Product.Price
etc

but it seems to me that there should be a way of avoiding that extra 
code.

I also tried:

Product.#{field_to_show}

and it didn''t work (no method error)

Thansk for the help.

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I think that Product["#{params[:foo]}"] should do the work.

Roland

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On 6/9/06, zero halo <zerohalo@gmail.com> wrote:
> That probably isn''t the right title for this topic, but
I''m not sure how
> else to explain in succintly. I''m sorry if this is obvious but I
> couldn''t find the answer in the Ruby/Rails docs.
>
> How do I use a variable as a substitute for a method/field, so that I
> can call the object with the variable that contains the method name.
Generally it''s done by

obj.send(var)

Method calls are just messages send to objects, so you can use the
#send method to do that.

In ActiveRecords''s case, there''s a special convenience method
that should work:

ar_instance[var]
>
> For example, say I have the object Product, that has methods Price,
> Last_Price, Average_Price.
>
> I want to be able to return the value of either of those three fields
> based on the user selection. Ie, user selection is stored in
> params[:foo], which I assign to variable field_to_show, and I want to be
> able to call:
>
> Product.field_to_show
>
> which should output Product.Price (if params[:foo] contained
''Price'')
>
> Currently this gives a no method error.
>
> I know that I can do
> case params[:foo]
>     when "Price"
>          Product.Price
> etc
>
> but it seems to me that there should be a way of avoiding that extra
> code.
>
> I also tried:
>
> Product.#{field_to_show}
>
> and it didn''t work (no method error)
>
> Thansk for the help.
>
> --
> Posted via http://www.ruby-forum.com/.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
>

-- 
-Alder

Alder Green wrote:
> Generally it''s done by
> 
> obj.send(var)
> 
> Method calls are just messages send to objects, so you can use the
> #send method to do that.
> 
> In ActiveRecords''s case, there''s a special convenience
method that
> should work:
> 
> ar_instance[var]
Both of those worked. Thanks, Alder.

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