[Zope-dev] Re: zope.sqlalchemy, integration ideas

[Brian Sutherland]

On Fri, May 30, 2008 at 03:49:46PM +0200, Martijn Faassen wrote:
> Brian Sutherland wrote:
> [snip]
>> I'll note that there is a difference between where things are published
>> (IAbsoluteURL) and where you should go to find their canonical
>> representation.
>>
>> One problem I've found with using IAbsoluteURL and location proxies is
>> getting the object directly from the database. In this situation you
>> don't have an LocationProxy and IAbsoluteURL doesn't work.
>>
>> It's pretty nasty when IAbsoluteURL sometimes works and sometimes
>> doesn't for what essentially is the same object.
>
> Agreed, we should ideally always get our objects from the db already 
> properly wrapped in a location proxy (or providing ILocation directly). I 
> think we can do this with containers based on relations; those containers 
> are under our control after all.

I've just decided to jettison IAbsoluteURL and make a new interface
ICanonicalURL. The adapters for ICanonicalURL are available anywhere
without specially wrapping the object in a location proxy.

> Is a direct one on one relation possible in SQLAlchemy? I.e. an object foo 
> that has an attribute 'bar' that is another ORM-ed object. If so we also 
> need to take care of that case somehow.

This was a problem with sqlos containers as well. It gets nasty quickly.
Say you have 2 containers, of people and addresses. Also people can have
an address.

So you can get to an address in 2 different ways:

    /adresses/address1
    /people/person1/address1

What should the url for address1 be? I'd vote for /adresses/address1.
But due to the LocationProxy, you'll get different results for different
IAbsoluteURL calls depending on how you traversed to the object.

> This is the "it should work like ZODB-backed objects" pattern I've been 
> trying to follow as a design guideline. Since for contained objects I can 
> always get the URL, it should work that way for RDB-based contained objects 
> too.

I'm not sure it's worthwhile following the "it should work like
ZODB-backed objects" pattern.

>
> Regards,
>
> Martijn
>
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-- 
Brian Sutherland