[sqlalchemy] Re: column 'title' used in key specification without a key length
On Mar 1, 2008, at 11:36 AM, Victor Lin wrote: It says that I should set the length of key of title. I know I can solve this problem by setting the length of key. But the problem is : How to set the length for key? I can't find method to do so in document. try using : from sqlalchemy.databases.mysql import MSText MSText(length=somelength) since length is not standard for the Text type. --~--~-~--~~~---~--~~ You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalchemy@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en -~--~~~~--~~--~--~---
[sqlalchemy] new joined-table polymorphic helpers available in trunk
hey alchemers -
I want to direct your attention to some new features in trunk which
I'll also be demonstrating at this years Advanced SQLAlchemy tutorial.
these features apply primarily to joined-table inheritance scenarios,
and are in response to the need to specify criterion against
subclasses as well as to join to/from joined-table classes where a
specific subclass is required.
I've put some new docs at
http://www.sqlalchemy.org/docs/04/mappers.html#advdatamapping_mapper_inheritance_joined_querying
.
the two methods are with_polymorphic() and of_type().
with_polymorphic() may very well replace the need for select_table in
almost all cases, and it creates the joins for you. It allows
filtering criterion to be against subclasses, *and* allows the mapper
to load the full subclass instance without the need for a second query
against the joined table.
Assume the usual Person / Engineer(Person) / Manager(Person) example :
# query for Person objects, but specify criterion against Engineer
session
.query
(Person
).with_polymorphic(Engineer).filter(Engineer.engineer_name=='dilbert')
# query for Person objects but specify criterion against both Manager
and Engineer
session.query(Person).with_polymorphic([Engineer,
Manager]).filter(or_(Engineer.engineer_name=='dilbert',
Manager.manager_name=='dogbert'))
# eagerly load all joined-table subclasses
session.query(Person).with_polymorphic('*').filter(...filter on any
table..).all()
of_type() is an operator applied to relations and is useful for
joining, as well as the any() and has() operators. Assume Company
objects contain a collection called employees' which contains Person
objects:
# join from Company to Engineer along its employees relation
session
.query
(Company
).join
(Company
.employees.of_type(Engineer)).filter(Engineer.engineer_name=='dilbert')
# query for Company objects where dilbert works
session
.query
(Company
).join
(Company
.employees.of_type(Engineer).any(Engineer.engineer_name=='dilbert'))
So once again, all of these methods are designed to work with joined-
table inheritance. For concrete inheritance, we still arent
generating those UNIONs automatically, though you can use
with_polymorphic() if you send along a second argument which is a
selectable to pull rows from.
If folks want to get on trunk and test out these features, that would
be great.
- mike
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[sqlalchemy] Re: new joined-table polymorphic helpers available in trunk
I want to direct your attention to some new features in trunk which
I'll also be demonstrating at this years Advanced SQLAlchemy
tutorial.
these features apply primarily to joined-table inheritance
scenarios, and are in response to the need to specify criterion
against subclasses as well as to join to/from joined-table classes
where a specific subclass is required.
I've put some new docs at
http://www.sqlalchemy.org/docs/04/mappers.html#advdatamapping_mappe
r_inheritance_joined_querying .
the two methods are with_polymorphic() and of_type().
with_polymorphic() may very well replace the need for select_table
in almost all cases, and it creates the joins for you. It allows
filtering criterion to be against subclasses, *and* allows the
mapper to load the full subclass instance without the need for a
second query against the joined table.
Assume the usual Person / Engineer(Person) / Manager(Person)
example :
# query for Person objects, but specify criterion against Engineer
session
.query
(Person
).with_polymorphic(Engineer).filter(Engineer.engineer_name=='dilber
t')
# query for Person objects but specify criterion against both
Manager and Engineer
session.query(Person).with_polymorphic([Engineer,
Manager]).filter(or_(Engineer.engineer_name=='dilbert',
Manager.manager_name=='dogbert'))
# eagerly load all joined-table subclasses
session.query(Person).with_polymorphic('*').filter(...filter on
any table..).all()
let me see if i got it... does this mean that, in the a-b-c-.. mapper
hierarchy i do not have anymore to use the selecttable=
a.outerjoin(b) (and eventualy .outerjoin(c) etc) on each level, but
instead use only one mapper (a) for everything, just having different
query.with_poly(x) for each subclass x?
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