Get count, average, min, max values from model field using Django Aggregate

Django queries help to create, retrieve, update and delete objects. But sometimes we need to get summered values from the objects. Then a Simple solution is to use Django aggregate feature Here are simple examples of how to use aggregation.

app/models.py

class company(models.Model):

    name=models.CharField(max_length=20)

    est=models.IntegerField(max_length=4)

class feature(models.Model):

    name=models.CharField(max_length=20)

class device(models.Model):

    name=models.CharField(max_length=20)

    Code=models.IntegerField()

    Company=models.ForeignKey(company)

    features=models.ManyToManyField(feature)

To perform Min Max and Avg on specific column

 

>>> from django.db.models import Avg, Max, Min, Sum
>>> device.objects.all().aggregate(Avg('price'))
    {'price__avg': 12234.0}
>>> device.objects.all().aggregate(Max('price'))
    {'price__max':587961 }
>>> device.objects.all().aggregate(Min('price'))
{'price__min': 01245}

To know the children count of a foreign key field. 

>>> Comp_Devices=company.objects.annotate(no_of_devices=Count('device'))
>>> Comp_Devices[0].no_of_devices
36
>>> Comp_Devices[0].name
u'Micro'
>>> Comp_Devices[1].no_of_devices
1

the same procedure can be followed for ManyToMany field Columns

>>> Dev_features_count = device.objects.annotate(num=Count('features'))

>>> Dev_features_count[0].num

3

>>> Dev_features_count[1].num

2

>>> 

 

You can perform some complex queries like

To know the devices which have more than two features

>>> Dev_features= device.objects.annotate(num=Count('features')).filter(num__gt=2)

>>> Dev_features[0].num

3

>>> 
    By Posted On
SENIOR DEVELOPER at MICROPYRAMID

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