python - Average over a relationship in django -

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i have 2 entities, namely project , issue defined followed:

class project(models.model):  class issue(models.model):     project = models.foreignkey(project, related_name='issues')     progress = models.integerfield(default=0)

i'd have progress method in project model return average of related issue progress.

i tried following i'm getting related issue list.

def progress(self):     return self.issues.annotate(models.avg('progress'))

thanks help.

what want is:

def progress(self):     aggregate = self.issues.aggregate(models.avg('progress'))     return aggregate['progress_avg']

if intend show progress of each project in project list view, use like:

for project in project.objects.annotate(progress_avg=models.avg('issues__progress')):     print project.progress_avg

the latter example better list view, since avoids n+1 problem (1 aggregation query each project in list).


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