Re: Queries and OO

From: frebe (fredrik_bertilsson_at_passagen.se)
Date: 01/16/05 

Date: 16 Jan 2005 09:30:18 -0800

> I'd say that querying is rather about some specific implementation
than
> modeling.

Lets say we have an application for order administration. Wouldn't it
be necessary to be able to find orders by customer, by delivery date,
by status, by product and combinations of these criterias? Not having a
query mechanism would force you to have a lot of maps and sorted sets
containing the customer objects. And when combined searches are done,
decisions about in what order to use the containers have to be made.

Queries is a way to decouple how objects are mapped into a container,
from how the objects are retrieved from the container. When you are
making software, new feature request forces you to retrieve objects in
new and different ways all the time. A hard-wired solution with
pre-defined search paths is mostly not possible.

> I might need no queries even if I do use a database.

True, long time ago there were database types without query
capabilites. It was possible to make working applications in that era
too. But maybe the query capabilities was one of the reasons behind the
success story of relational databases.

> What could be so intriguing in a set of tables?

Many application vendors find relational databases and tables an
extremly important component in their solution. If we want the
application to collaborate with a database, we should model this too.
Fredrik Bertilsson
http://butler.sourceforge.net

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