automatic type casting of query parameters in finds

I'm new to ruby on rails and am using active record 3 to create some
object models on top of a postgres db.

I have an Environment record with a :name attribute that maps to the
:name column of type :string. When I do Environment.find_by_name( "abc"
), everything works as expected. However, when I do
Environment.find_by_name( 123 ), my code breaks with the following
error:

ERROR: operator does not exist: character varying = integer
(ActiveRecord::StatementInvalid)
LINE 1: ...nts"."purpose" = 'test' AND "environments"."name" = 123)
LI...
                                                             ^
HINT: No operator matches the given name and argument type(s). You
might need to add explicit type casts.

So my question is, if activerecord knows the type of the :name column
(:string), then why doesn't it automatically call to_s on the :name
parameter to avoid this issue?

I have a work around right now that overrides find, and explicitly does
this type casting, but I'm guessing there is a cleaner way to achieve
this behavior.

Thanks,
Alex