On 08/30/2010 16:06, Michael Bayer wrote:
On Aug 30, 2010, at 5:59 AM, Julien Cigar wrote:Hello, Quick question, is there a way to use .with_polymorphic() on a Query with existing criterion ? I have the case where I have 2 queries with the same criteria where one of those queries is a count(*). I would like to avoid multiple LEFT JOIN because criteria in the count(*) query because they are not necessary (criteria relate to the base class).with_polymorphic() is a pretty limited feature at the moment which is why it only works against a single entity and only works up front.
limited.. but pretty useful in my case :)
I haven't added this to the main docs but the strategy to get a polymorphic query of any style is to use the individual Table objects and construct the joins as needed, like: sess.query(Person).join((engineers_table, Person.id==engineers_table.c.id))...
.outerjoin(), no ?
very often if i just need information against the subclass, I'll leave out the base entirely. It's all about placing the minimal number of tables in the FROM clause: sess.query(engineers_table.c.id).join((machine_table, engineers_table.c.id==machine_table.c.engineer_id))...
In fact I'm writing a CMS where I allow the user to select which subclasses is queried within a given container, this allow the use to add default ordering of a container, apply filters, etc
I ended with something like (I use the .whereclause of the first query):
q = model.Content.query.published().in_container(id)
( ... )
c.count_filtered = q.count()
q2 = model.Content.query.with_polymorphic_content(id).\
filter(q.whereclause)
I have a custom Query object with the following:
@staticmethod
def get_polymorphic_content(src):
if not isinstance(src, Content):
src = Content.query.get(src)
if not src.polymorphic_loading:
# TODO : default polymorphic loading strategy ..
return None
elif src.polymorphic_loading == 'y':
return '*'
elif src.polymorphic_loading == 'c':
polymorphic_types = [i.id for i in src.polymorphic_children]
polymorphic_map = orm.class_mapper(Content).polymorphic_map
return [polymorphic_map[i].class_ for i in \
polymorphic_types]
else:
return None
def with_polymorphic_content(self, src):
cls = self.__class__.get_polymorphic_content(src)
return self if not cls else self.with_polymorphic(cls)
Thanks,
Julien
Thanks, Julien -- No trees were killed in the creation of this message. However, many electrons were terribly inconvenienced. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. <jcigar.vcf>
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