[storm] Best way to implement One-to-one relationships?

[James Henstridge]

On Fri, Aug 28, 2009 at 6:19 PM, Mac Ryan<quasipedia at gmail.com> wrote:
> On Fri, 2009-08-28 at 10:25 +0800, James Henstridge wrote:
>> Hi Mac,
>>
>> I saw your question on IRC in my scrollback yesterday, but you quit
>> before I was awake.
>>
>> ...
>>
>> Hope this helps.
>>
>> James.
>
> Wow... it's the first time it ever happened to me to be "chased" from IM
> to ML from somebody wishing to help... I feel like a spoiled brat
> now! :)
>
> Anyhow, thank you for your answer after a 1to1 comparison between the
> tutorial and my code I came to the same conclusion.
>
> Somehow I expected Storm to behave differently (i.e.: introspect the
> code to the point in which it would have created the object for me "on
> the fly", (or retrieve it from the store if an existing primary key for
> the "dependent table" was given). I do not why I believed so... it
> seemed for me the most logical way to work, but I suppose that since
> "explicit is better than implicit" it makes more Python-sense to work as
> it is...

Storm doesn't perform any introspection of your database schema -- it
only works with the information you provide on the Python side.

And the Reference() type is used for much more than a direct one to
one relationship (often it is many to one), so automatically creating
a row in the second table when one is created in the first does not
make sense from a generic standpoint.  In many cases, the Reference
might be left NULL or linked to an existing object.

For your case, if you always want a row created in the second table
when you create one in the first table, I'd suggest doing so in the
__init__() method of the first class.  Something like:

    class TableA(object):
        _storm_table__ = 'tablea'
        ...
        def __init__(self):
            self.extra_fields = TableB()

That way any TableA row created from Python and added to the store
will have a matching TableB row.

James.