#3566: Proposal of ORM extension -- aggregationu
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Reporter: Honza Král <[EMAIL PROTECTED]> | Owner: adrian
Status: new | Component: Database wrapper
Version: SVN | Keywords: orm aggregation
group by
Stage: Unreviewed | Has_patch: 0
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For origin and some discussion see http://groups.google.com/group/django-
users/browse_frm/thread/fc58fbe409a6f098/1110c688e1af58d2
I would like to see an addition to the django ORM - many people has asked
for aggregation. Do you think Django should have aggregation support?
I would like to add it in a similar fashion that {{{ ValuesQuerySet }}} is
implemented (a subclass to {{{QuerySet}}} with minor changes to how query
is constructed and results are returned) - if we add a {{{
AgreggateQuerySet }}} that would:
* be create from simple {{{ QuerySet }}} by a call to {{{
aggregate(group_by=(), max=(), min=(), avg=(), sum=(), count=False) }}},
where:
* {{{group_by}}} is a list of fields on which to aggregate, these will
be part of the result, if empty the whole query will be grouped
* If {{{count}}}, then {{{COUNT(*)}}} will be computed and included
* {{{sum, max, min}}} and {{{avg}}} will contain a list of fields on
which to call {{{SUM(), MAX(), MIN()}}} or {{{AVG()}}} respectively
* will be a valid queryset
* {{{filter()}}} will result in limiting the result by appending
conditions to the {{{ HAVING }}} clause etc.
* {{{aggregate()}}} will probably add fields to individual aggregation
functions.
{{{ queryset.count()}}} would become identical to
{{{queryset.aggregate(count=True)['count']}}}
Example:
{{{
>>> quseryset = Model.objects.all()
>>> queryset.aggregate( group_by=( 'name', 'city' ), sum=( 'pay',
'some_other_field' ), avg=( 'pay', 'age' ), count=True )
[
{
'group_by' : { 'name' : 'John Doe', 'city' : 'Prague', }
'sum' : { 'pay' : 50000, 'some_other_field' : 10000 },
'avg' : { 'pay' : 10000, 'age' : 30 },
'count' : 5,
},
{
'group_by' : { 'name' : 'Jane Doe', 'city' : 'Paris', }
'sum' : { 'pay' : 300000, 'some_other_field' : 10 },
'avg' : { 'pay' : 100000, 'age' : 32 },
'count' : 3,
},
]
}}}
There are a few problems I haven't thought through and would like
comments:
* how to deal with grouping by foreign key? the best seems to include
the whole object in the result, not just the ID. (isn't it too magical?)
* how to specify ordering?
* how to best present the results? originally I thought that fields in
{{{group_by}}} will be on the same level as {{{min}}} or {{{max}}}, but
Tim Chase pointed out that it could clash if the model has a field named
{{{min}}} .
I will start working on this as soon as I am sure about the interface. Any
comments and help would be greatly appreciated.
--
Ticket URL: <http://code.djangoproject.com/ticket/3566>
Django Code <http://code.djangoproject.com/>
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