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

>>> 

Subscribe To our news letter

Subscribe to our news letter to receive latest blog posts into your inbox. Please fill your email address in the below form.
*We don't provide your email contact details to any third parties
Latest Comments
Related Articles
Inclusion Tags Ashwin Kumar

Django’s template system comes with a wide variety of built-in tags and filters designed to address the presentation logic needs of your application. You can ...

Continue Reading...
Sendgrid Inbound Email Parsing with django Nikhila Mergu

Using the Inbound parse webhook, we can parse the contents, attachments of an incoming email.

Inbound Parse API follows 3 steps:
1. sending an ...

Continue Reading...
Querying with Django Q objects Dinesh Deshmukh

Querying with Django Q objects: Q object encapsulates a SQL expression in a Python object that can be used in database-related operations. Using Q objects ...

Continue Reading...