I have 2 tables Cluster and Node, each having a volume_limit and
volume_count column in it.
To atomically check and increment the volume count for a Cluster and Node I
do the following
updated = Cluster.objects.filter(id=cluster_id,
volume_count__lt==F('volume_limit')).update(volume_count =
F('volume_count')+1)
if not updated:
raise Validation('limit reached ......')
updated = Node.objects.filter(id=node_id,
volume_count__lt==F('volume_limit')).update(volume_count =
F('volume_count')+1)
if not updated:
Cluster.objects.filter(id=cluser_id).update(volume_count =
F('volume_count')-1)
raise Validation('limit reached ......')
I am wondering if there is way to do both of this atomically?
Basically I want to
1. create a query for Cluster, Node, etc, N such objects/tables queries,
that each filter match one row by pk and volume_count__lt=F('volume_count')
2. Check that the union of all these queries translates to exactly N
objects, one for each Object/Table. i.e. the counts are within limit for
each object/table
3. Do a volume_count=F('volume_count')+1 for all those objects/table
together.
How do I do this?
Thanks,
Sarvi
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