This seems to work
Node.objects.values('cluster').annotate(volume_left=min(F('cluster__volume_limit')-F('cluster__volume_count'),
Sum(F('volume_limit')-F('volume_count'))))
<QuerySet [{'cluster': 1, 'volume_left': 8}, {'cluster': 1, 'volume_left':
8}, {'cluster': 2, 'volume_left': 20}, {'cluster': 2, 'volume_left': 20}]>
Do I have it right? Just wanted to confirm.
Thanks
On Saturday, July 1, 2017 at 5:41:20 PM UTC-7, sarvi wrote:
>
>
> Django Verion: 1.11.1
>
> My models
>
> class Cluster(models.Model):
>
> ....
>
> volume_limit = models.IntegerField('Cluster Volume Count Limit')
>
> volume_count = models.IntegerField('Cluster Volume Count', default=0)
>
> ....
>
>
> class Node(models.Model):
>
> cluster = models.ForeignKey(Cluster, related_name='cluster_nodes',
> on_delete=models.PROTECT)
>
> volume_limit = models.IntegerField('Node Volume Count Limit')
>
> volume_count = models.IntegerField('Node Volume Count', default=0)
>
>
> My query
>
> nodes = Node.objects.filter(....)
>
> intermediatestep =
> nodes.objects.annotate(volume_left=F('volume_limit')-F('volume_count')).values('cluster__id').annotate(cluster_volume_left_sum=
> Sum('volume_left'))
>
>
> Error:
>
> File
> "/Users/sarvi/virtenv/toothless/lib/python2.7/site-packages/django/db/models/expressions.py",
>
> line 471, in resolve_expression
>
> return query.resolve_ref(self.name, allow_joins, reuse, summarize)
>
> File
> "/Users/sarvi/virtenv/toothless/lib/python2.7/site-packages/django/db/models/sql/query.py",
>
> line 1481, in resolve_ref
>
> return Ref(name, self.annotation_select[name])
>
> KeyError: 'volume_left'
>
>
> My ultimate Goal:
>
> What I am trying to achieve is to get from a
>
> 1. filtered query of Nodes, to calculate
> volume_left=F('volume_limit')-F('volume_count') for each node
>
> 2. then group by cluster and sum up what volume_left in each node to
> cluster_volume_left_sum for each cluster.
>
> 3. Then get a cluster level
> cluster_volume_left=F('volume_limit')-F('volume_count'),
>
> 4. Then calculate at the cluster level Min(0,
> F('cluster_volume_left')-F('volume_left__sum'))
>
>
> I am obviously stuck way earlier :-)
>
>
> From what I read of the documentation and Stackoverflow this should be
> possible
>
>
> Any pointer on what I am doing wrong here would be of great help.
>
>
> Thanks,
>
> Sarvi
>
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