[Zope-DB] Relational Databases in Zope 2 and Zope 3

[Tres Seaver]

Smith, Neil (Worcester) wrote:
> The point of the dtml-sqlgroup and dtml-sqltest is surely to provide a nice
> way of handling the case where you don't pass in the parameter, so it
> doesn't render the WHERE, AND, = etc.  And it does this quite well.
> 
> If you remove it, then you'll need either an exponential number of SQL
> methods and some logic before it to decide which to call, or you'll have to
> fill the SQL method with even more confusing dtml-if statements, or you'll
> have to have your SQL something like:
> 
> WHERE (
>    <dtml-sqlvar parameter_1 type=..> is null or 
>    column_1 = <dtml-sqlvar parameter_1 type=..>
> ) and (
>    <dtml-sqlvar parameter_2 type=..> is null or 
>    column_2 = <dtml-sqlvar parameter_2 type=..>
> )
> 
> which again seems more confusing, (and in fact doesn't work if a parameter
> is a number rather than a string).

The dilemma here is similar to the classic one between OLAP and OLTP: 
arbitrarily flexible queries are death to transactional throughput.

If your application *needs* this flexibility, then you *can't* take 
advantage of prepared queries anyway, as there is no "canonical" version
of the query to prepare.  There are is *huge* space of applications, 
however, which *could* benefit from prepared queries;  for them the 
price of DTML's flexibility is both painful and unneccessary.

Tres.
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Tres Seaver                                tseaver at zope.com
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