Thanks. But using a CASE clause becomes objectionable in exactly those cases
where I would want to have the DB do the sorting — i.e. where the table is
big enough that just sorting the result set in python code using array index
(rows.sort(key=lambda row: values.index(row[0]))) would be a Bad Thing
(since the key function is O(n)).
But then, sorting on a reversed enumeration dict in python is
algorithmically the same as the temp table approach. Something like:
rows = session.query(...).all()
value_to_index = dict((v,k) for (k,v) in enumerate(values))
rows.sort(key=lambda value: value_to_index[value])
so I suppose that's the cleanest solution here, unless one really prefers to
make the DB do the sorting.
I believe all of these approaches will gracefully handle the case where
values are not unique (the order will just be arbitrary within each group
with the same value).
Regards,
- Gulli
On Thu, Feb 26, 2009 at 9:40 AM, Ants Aasma ants.aa...@gmail.com wrote:
import sqlalchemy
def index_in(col, valuelist):
return sqlalchemy.case([(value,idx) for idx,value in enumerate
(valuelist)], value=col)
session.query(C).filter(C.someattr.in_(valuelist)).order_by(index_in
(C.someattr, valuelist))
Don't try to do this with huge lists of items.
On Feb 25, 5:53 pm, Gunnlaugur Briem gunnlau...@gmail.com wrote:
Hi all,
having a x IN y query, with y supplied as input to the query:
session.query(C).filter(C.someattr.in_(valuelist))
is there a way to tell SQLAlchemy to order the results according to
valuelist? I.e. not by the natural order of someattr, but by the
arbitrary order seen in valuelist? E.g.:
session.add(C(someattr='Abigail'))
session.add(C(someattr='Benjamin'))
session.add(C(someattr='Carl'))
valuelist = ['Benjamin', 'Abigail']
q = session.query(C).filter(C.someattr.in_(valuelist)).order_by(clever
(valuelist))
q.all()
# returns [C('Benjamin'), C('Abigail')]
The solution I can think of is to create a temporary table with
sess.execute('create temp table ...'), insert the valuelist into that
temp table along with a sequence index, join to that temporary table
and order by its index. Is there a less kludgy way?
Regards,
- Gulli
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