how use annotation Instead loop on filter

Question

i use a table Bid in this table have multi fields and a field named user other hand have a Dealer table that save users in Dealer_serializer i have a bids_count serializer Method Field that return each user count in Bid table i want use annotate instead of loop over filter! to get each user how many in Bid Table. if my idea not true explain me what exactly doing annotation?

class Dealer(User):
    car_exhibition = models.CharField(max_length=200, blank=True, null=True)
    phone = models.CharField(max_length=11, blank=True, null=True)
    city = models.ForeignKey('locations.City', blank=True, null=True)
    address = models.TextField(max_length=500)

class Bid(models.Model):
    auction = models.ForeignKey('Auction')
    user = models.ForeignKey('users.User')
    step = models.BigIntegerField()
    price = models.BigIntegerField()

created_time = models.DateTimeField(auto_now=True)

It's better to provide a code snippet rather than describing it. Please paste your models. — Sergey Pugach
– Sergey Pugach, Commented Dec 17, 2018 at 6:20
Dealer inherit from django user table that have username , id, ... — amir boluri
– amir boluri, Commented Dec 17, 2018 at 6:54

Sergey Pugach · Accepted Answer · 2018-12-17 07:09:42Z

1

I can't find the relation of your Dealer with Bid. But for User you can use annotation:

User.objects.annotate(bids_count=Count('bid')).values('id', 'bids_count')

As a result you will have:

<QuerySet [{'id': 1, 'bids_count': 3}, {'id': 2, 'bids_count': 10}, ..., >

Where id is user_id and bid_count is how many Bids are related to User with that id. I hope this is what you are going to achieve. Please comment in case of any questions.

answered Dec 17, 2018 at 7:09

Sergey Pugach

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