Fantastic, it works just the way I was hoping. Thanks.
I ended up using the mapper rather than taking the declarative route
(especially since I'm extracting table structures via metadata), but
as far as I can tell it all works fine - just in case anyone wants to
see an example of it (missing some of the detail around metdata &
mapper):
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.orm.properties import ColumnProperty
mytable = Table('mytable', metadata, autoload=True)
class MyClass(object):
def __init__(self, name):
# using '_' column prefix, see mapper call below
self._name = name
class MyComparator(ColumnProperty.ColumnComparator):
def __eq__(self, other):
return func.lower(self.__clause_element__()) == func.lower
(other)
mapper(MyClass, mytable, column_prefix='_', properties={
'name':synonym('_name', map_column=True,
comparator_factory=MyComparator)
})
On Nov 18, 1:41 am, Michael Bayer <[EMAIL PROTECTED]> wrote:
> On Nov 17, 2008, at 7:50 AM, Iain wrote:
>
>
>
>
>
> > I was wondering if anyone is aware of a way that I can customize the
> > way query filters are written - possibly by some sort of customization
> > of table columns?
>
> > The issue is that I have some odd data/column types that can't be
> > compared directly. That is, "SELECT * WHERE column1=value1" will not
> > work - instead, I need to do "SELECT * WHERE user_func(column1)
> > =user_func(value1)" or in some instances I want to do "SELECT * WHERE
> > column2=user_func(value2)".
>
> > So rather than everyone who writes queries having to remember to write
> > these out as text or such, it'd be good if I could tell sqlalchemy to
> > always re-write the queries that way whenever a user tests for
> > equivalence on the relevant columns.
>
> > Hope that makes sense!
>
> you would implement this using a custom comparator class. Its a very
> new feature that these are fully customizable, so this is how it looks
> right now:
>
> from sqlalchemy import *
> from sqlalchemy.orm import *
> from sqlalchemy.ext.declarative import declarative_base
> from sqlalchemy.orm.properties import ColumnProperty
>
> Base = declarative_base()
>
> class MyComparator(ColumnProperty.ColumnComparator):
> def __eq__(self, other):
> return func.lower(self.__clause_element__()) ==
> func.lower(other)
>
> class MyClass(Base):
> __tablename__ = 'mytable'
> id = Column(Integer, primary_key=True)
> name = column_property(Column(String(50)),
> comparator_factory=MyComparator)
>
> sess = sessionmaker()()
>
> print sess.query(MyClass).filter_by(name='SomeName').statement
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