django - Generating a single queryset with filtered summary data across a foreign key? -


i have small django project learn (it's web ui rancid backup software) , i've run problem.

the model app defines devices, , devicegroups. each device member of group , has couple of state flags - enabled, successful - indicate if operating correctly. here's relevant bits.

class devicegroup(models.model):     group_name = models.charfield(max_length=60,unique=true)  class device(models.model):     hostname = models.charfield(max_length=60,unique=true)     enabled = models.booleanfield(default=true)     device_group = models.foreignkey(devicegroup)         last_was_success = models.booleanfield(default=false,editable=false)

i have summary table on front 'dashboard' page, shows list of groups, , each group, how many devices in it. i'd show number of active devices, , number of failing (i.e. not last_was_success) devices per-group. plain device count available through foreignkey field.

this seems kind of thing annotate for, not quite. , actually, i'm not sure how i'd raw sql either. 3 queries , lookup afterwards, or subqueries.

so - possible 'nicely' in django? or alternatively, how do joining again in template or view? object passed template simply:

device_groups = devicegroup.objects.order_by('group_name')

currently, , don't think can add fields onto queryset results "manually", can i? i.e. it's not dict or similar.

i think must use 

device_groups = devicegroup.objects.all().order_by('group_name')

or

device_groups = devicegroup.objects.filter(condition).order_by('group_name')

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