Nested serializers and data representation - django

Question

Working on a django project I am a bit stuck on data representation through APIs. In fact when designing models the data model is quite stratighforward : I have a one to many relationship A--> B
therefore I have added a FK to object B.
Object B has a boolean attribute "active".
I would like to make an API call to list all A objects having at least one assoicated object B with active = true.
The api could be like this :
/api/objectA/?ObjectB.active=True
Here is my code :
Models :
from django.contrib.postgres.fields import ArrayField
from django.core.exceptions import ValidationError
from django.db import models
from django.db.models.signals import pre_save
from django.dispatch import receiver
class Startup(models.Model):
header = models.CharField("Header", max_length=255)
title = models.CharField("Title", max_length=255)
description = models.CharField("description", max_length=255)
# TODO Change this to options instead of array
tags = ArrayField(models.CharField(max_length=10, blank=True), size=5)
# TODO Images to be stored in aws only url will be in DB
card_image = models.ImageField(upload_to='media/images/cards')
logo_image = models.ImageField(upload_to='media/images/logos')
main_img = models.ImageField(upload_to='media/images/main', null=True)
createdAt = models.DateTimeField("Created At", auto_now_add=True)
def __str__(self):
return self.title
class Investment(models.Model):
# TODO change the name of Investment to fund round in back and front
# TODO all price to be checked for max digits and decimal places
startup = models.ForeignKey(Startup, related_name='startup_investments', on_delete=models.CASCADE, default="1")
# Use the related_name as a serializer bale for investments inside startup serializer
Investment_title = models.CharField("Investment_title", max_length=255, default="Missing Title")
collected_amount = models.DecimalField(max_digits=12, decimal_places=2)
goal_percentage = models.IntegerField(default=0)
number_of_investors = models.IntegerField(default=0)
days_left = models.IntegerField()
active = models.BooleanField(default=False)
# TODO Need to update this to prevent linking to a non existing startup
createdAt = models.DateTimeField("Created At", auto_now_add=True)
def clean(self):
"""Validate that the startup does not have already an active Investment """
if self.active:
qs = Investment.objects.filter(active=True).filter(startup=self.startup)
if self.pk is not None:
qs = qs.exclude(pk=self.pk)
if qs:
raise ValidationError(message="An active investment already exists for this startup")
def __str__(self):
return self.Investment_title
Serializers :
from rest_framework import serializers
from .models import Startup, Investment
class InvestmentSerializer(serializers.ModelSerializer):
class Meta:
model = Investment
fields = ('id', 'Investment_title', 'collected_amount', 'goal_percentage', 'number_of_investors',
'days_left', 'active')
class StartupSerializer(serializers.ModelSerializer):
startup_investments = InvestmentSerializer(many=True, read_only=True)
class Meta:
model = Startup
fields = ('id', 'header', 'title', 'description', 'tags', 'card_image',
'logo_image', 'main_img', 'startup_investments')
Views :
from django_filters import rest_framework as filters
from rest_framework.viewsets import ModelViewSet
from rest_framework_extensions.mixins import NestedViewSetMixin
from .serializers import *
class StartUpViewSet(NestedViewSetMixin, ModelViewSet):
"""
Class that provides List, Retrieve, Create, Update, Partial Update and Destroy actions for startups.
It also include a filter by startup status
"""
model = Startup
queryset = Startup.objects.all()
serializer_class = StartupSerializer
class InvestmentViewSet(NestedViewSetMixin, ModelViewSet):
"""
Class that provides List, Retrieve, Create, Update, Partial Update and Destroy actions for Investments.
It also include a active and investment title
"""
model = Investment
serializer_class = InvestmentSerializer
queryset = Investment.objects.all()
filter_backends = (filters.DjangoFilterBackend,)
filterset_fields = ('active', 'Investment_title')
routers :
router = ExtendedSimpleRouter()
(
router.register(r'api/investments', views.InvestmentViewSet, basename='investment'),
router.register(r'api/startups', views.StartUpViewSet, basename='startup')
.register(r'investments', views.InvestmentViewSet, basename='startups_investment',
parents_query_lookups=['startup']),
)
Thanks for your help.

Answer 1

I would try something like this:
class StartUpViewSet(NestedViewSetMixin, ModelViewSet):
model = Startup
#queryset = Startup.objects.all()
serializer_class = StartupSerializer
def get_queryset(self):
Startup.objects.annotate(active_investments=Count('startup_investments', filter=Q(startup_investments__active=True)).filter(active_investments__gt=0)

Answer 2

Hello I am posting this answer hoping it will help others as I have spent two days to make this work!!
class ActiveStartupSerializer(serializers.ListSerializer):
def to_representation(self, data):
"""List all startups with one active investment"""
data = data.filter(startup_investments__active=True)
return super(ActiveStartupSerializer, self).to_representation(data)
class Meta:
model = Startup
fields = ('id', 'header', 'title', 'description', 'tags', 'card_image',
'logo_image', 'main_img', 'startup_investments')
class InvestmentSerializer(serializers.ModelSerializer):
class Meta:
model = Investment
fields = ('id', 'Investment_title', 'collected_amount', 'goal_percentage', 'number_of_investors',
'days_left', 'active')
class StartupSerializer(serializers.ModelSerializer):
startup_investments = InvestmentSerializer(many=True, read_only=True)
class Meta:
model = Startup
list_serializer_class = ActiveStartupSerializer
fields = ('id', 'header', 'title', 'description', 'tags', 'card_image',
'logo_image', 'main_img', 'startup_investments')