How to create a custom function inside django model?

Question

I have a django model

class UserInfluencerGroupList(models.Model):
    list_name = models.CharField(max_length=255)
    influencers = models.ManyToManyField(Influencer, blank=True)
    user = models.ForeignKey(MyUser, on_delete = models.CASCADE)

    def __str__(self):
        return self.list_name

and my views function is:

def get_lists(request,user_email):
    """Get all the lists made by user"""
    try:
        user_instance = MyUser.objects.get(email=user_email)
    except MyUser.DoesNotExist:
        return HttpResponse(json.dumps({'message':'User not found'}),status=404)

    if request.method == 'GET':

        influencers_list = UserInfluencerGroupList.objects.all().order_by('id').filter(user=user_instance)
        influencers_list = serializers.serialize('json',influencers_list, fields =['id','influencers','list_name'], indent=2, use_natural_foreign_keys=True, use_natural_primary_keys=True)

        return HttpResponse(influencers_list,content_type='application/json',status=200)
    else:
        return HttpResponse(json.dumps({'message':'No lists found'}), status=400)

Apart from the usual data from list I also want to calculate the total_followers, total_likes and total_comments of each influencer in the list. The influencer model has fields for total_likes, comments and followers.

How should I write a function to calculate and display it along with all the other data that the list is returning

if you want use this total_likes in the serializer you should use annotation in the query. — user8060120
– user8060120, Commented Jul 15, 2019 at 9:28
sorry, The question is a bit unclear. Do you want to know how to serialize influencers_list? — baskershu
– baskershu, Commented Jul 15, 2019 at 10:47
No, the influencers_list is already serialized. In the serialized data I want to send the count of followers of each influencer — Ahmad Javed
– Ahmad Javed, Commented Jul 15, 2019 at 10:49

Daniel Backman · Accepted Answer · 2019-07-16 05:30:41Z

1

You should consider to use Django Rest Framework if you want to return a json of your own choice or/and if you're about to create your own rest api.

Alternative is to create the json all manually, i.e build the dictionary and then use json.dumps.

(If you really want to go "manual" see answer Convert Django Model to dict)

The django serializers does not support what you want to do:

option for serializing model properties (won't fix)

Quote for not fixing: "I'm afraid I don't see the benefit of what you are proposing. The serialization framework exists for the easy serialization of Django DB-backed objects - not for the arbitrary serialization of _any_ object, and derived properties like the ones you are highlighting as examples don't add anything to the serialized representation of a DB-backed object..."

edited Jul 16, 2019 at 5:30

answered Jul 16, 2019 at 5:25

Daniel Backman

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