[Qgis-developer] QgsExpression: replacement for QgsSearchString

[Mayeul Kauffmann]

> > PostgreSQL is very strict about type conversions, Sqlite is not
> strict
> > at all and MySQL is somewhere in the middle. I have ended up with
> > these conversion rules:
> > - implicit conversions to desired types
> > - string->number conversions with invalid input return error
> > - arithmetic operators convert to numeric
> > - comparison with numeric type => numeric comparison 
Apparently my email is too late as this is already merged.
Still, IMHO, I would suggest that your rule be as close as possible to
the existing rules of one major RDBMS (am I correct in assuming that
your implementation is close to MySQL?), or you even better you may use
the rule of one existing DB wrapper.
You will probably get more consistent/robust results by trying to follow
as much as possible an existing standard instead of inventing Yet
Another Conversion Standard.
There will be use cases that you have not thought about yet. In front of
them, the Qgis community would ask "how standard x solves this problem?"
instead of "should we use standard x, y or z for this particular case?"

I am a big fan of postgres. But if you follow (say) MySQL 70 % of the
time, postgres 20 % of the time and your own rules the remaining 10%, I
would prefer if you try to use 100% MySQL-like rules.
My 2 cents.
Mayeul