On Feb 19, 7:07 am, ms <[email protected]> wrote:
> Hey,
>
> I want to realise some kind of virtual methods. I'll explain this with
> an example:
>
> Let's assume I've got a class called "Animal". Every "Animal" instance
> can have various attributes, which are not fix, they depend on the
> annotations associated within the "animal" database table. So I could
> create a method called "getAttribute()":
>
> animal = Animal.new()
> animal.getAttribute("WEIGHT")
>
> If there's an annotation called "WEIGHT", the weight is returned,
> otherwise "nil". The thing is: I don't want to write "getAttribute
> (XYZ)" each time to get the data. I want to write:
>
> animal.weight
>
> But there is no predefined accessor method called "weight". Some how,
> I must catch this. I've got two ideas, of which I'm not sure whether
> they make sense and can be implemented:
>
As Fred pointed out, method_missing is what you're thinking of; it's
what
AR uses to handle dynamic finders (find_by_x).
That being said, however, if you're referring to the fields in Ruby
code and
doing so often enough that a shorthand is good - you should really
just have
a DB field for it and be done.
Otherwise, you end up with a table like in this article:
http://thedailywtf.com/Articles/tblStaffDirectory.aspx
...which isn't so good.
Finally, if you're really just interested in attaching a few
"annotation"-style fields
to a model, take a look at serialized columns. Big warning: you gain
flexibility, but
at the cost of losing the ability to query values in SQL. I've used
serialized columns,
for example, to hold some fields that were imported by users from CSV
files and
then exported with the regular data fields to other CSV files. In that
case, my code
didn't care *what* the fields were, it just needed to store them.
--Matt Jones
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