Forum: Ruby on Rails Need an opinion on ActiveRecord vs.(?) duck typing

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Thiago A. (Guest)
on 2006-03-10 16:53
(Received via mailing list)
Rubysts,

First of all, I am pretty new to Ruby, Rails and even dynamic
languages in general. So please be patient with me. :-)

Disclaimer given, let's get to the guts.

I am trying to save a date/timestamp to my DB and comparing it with
one created outside of DB/ActiveRecord afterwards. The date is burried
inside an ActiveRecord object of mine and gets recorded together with
everything else from it. The problem is I don't know first hand the
exact type of the date object, due to duck typing. So, the date inside
an object could be virtually anything because it is passed to my
objects directly from client code.

But in the good real world it eventually boils down to two or three
types. Maybe the most significant are the Time and DateTime classes.
It happens that my (mysql, if that matters) DB schema represents this
particular date as a timestamp field and it is always (I think) mapped
back to a Time object by ActiveRecord. The problem happens when I need
to compare this ActiveRecord-converted Time object to a client-created
DateTime object. The == method simply returns false, always.

To get rid of the problem, the first solution I have thought of (and
implemented) is to insert a to_t method in the both classes, in order
to convert to a Time object. With this, every comparation I do after
the conversion. That way I am effectively comparing two Time objects
and the comparison is done correctly.

But that solution limits the number of classes my clients can insert
on the date field. I think it would be very unusual (though not
impossible) for someone to insert an Integer in it, but it wouldn't be
very strange to get a String. This other classes don't have the to_t
method defined and I would get a nice NoMethodError when I tryed to
call it. Although I almost control all client code, I wouldn't like to
remember to add a to_t method to every class that I manage to insert
on the date field. Besides that, I need to remember to call the to_t
method everytime.

The second solution I have thought of is to hide the date object
creation step inside the class. I could do that by redefining the
method that writes directly to the date field to receive all the
date/time components and then create the date object that will get
read in the future. But this way I have to change all current client
code. This can be done, but I would choose to do it only if I can't
find a better solution.

Any thoughts?

Cheers,

Thiago A.
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