Serialization of related pivot models with Django Rest Framework - django

Question

I am learning Django, and are using Django Rest Framework. In my application, I have three different models
Bar (holds information about a bar, has multiple beers through the BarBeer model)
Beer (holds information about a beer)
BarBeer (connection between a bar and a beer, has pivot fields such as alcohol, type, price and volume)
This is how the different models are defined:
class Bar(models.Model):
name = models.CharField(max_length=60)
location = models.PointField()
address = models.CharField(max_length=60)
description = models.TextField(default='')
beers = models.ManyToManyField('api.Beer', through='api.BarBeer')
class Beer(models.Model):
name = models.CharField(max_length=60)
alcohol = models.FloatField(default=0)
class BarBeer(models.Model):
bar = models.ForeignKey(Bar, on_delete=models.CASCADE)
beer = models.ForeignKey(Beer, on_delete=models.CASCADE)
price = models.FloatField(default=0)
type = EnumField(Type, default=Type.Cask)
volume = models.IntegerField(default=0)
Now I want to serialize a given bar with all the beers for that particular bar including the extra fields in the pivot model BarBeer. For example, below is what I'd like the output to be (note the extra three fields on the beer, that comes from the BarBeer model):
{
"id": 1,
"name": "A bar",
"beers": [
{
"id": 1,
"name": "Ship Full of IPA",
"alcohol": 6.5,
"type": "bottle",
"price": "35",
"volume": "33"
}
]
}
I can't figure out how to get the extra fields from the pivot model as part of the serialized output. This is what my serializer looks like right now:
class BarDetailsSerializer(serializers.ModelSerializer):
class Meta:
model = Bar
fields = ('id', 'name', 'beers')
depth = 3

Answer 1

Firstly beers = models.ManyToManyField('api.Beer', through='api.BarBeer') this field is unneccessary, because you have already created a table named BarBeer. ManyToManyField means adding exra table. So, if we assume this field is not exist and you have BarBeer table, you can do this with using BarBeerSerializer like that:
serializers.py
class BarBeerSerializer(serializers.ModelSerializer):
name = serializers.SerializerMethodField()
alchol = serializers.SerializerMethodField()
class Meta:
model = BarBeer
fields = ['id','name','alchol','type','price','volume']
def get_name(self,obj):
return obj.beer.name
def get_alchol(self,obj):
return obj.beer.alchol
class BarSerializer(serializers.ModelSerializer):
beers = serializers.SerializerMethodField()
class Meta:
model = Bar
fields = ['id', 'name', 'beers']
def get_beers(self,obj:Bar):
beers = obj.barbeer_set.all()
return BarBeerSerializer(beers,many=True).data
If there is an error, please ask it on comment.

Answer 2

One way to do this is you can create a custom serializer for the BarBeer model and pass the other two models serializers in it something like :~
class BarDetailsSerializer(serializers.Serializer):
bar = BarSerializer()
beer = BeerSerializer()
price = serializers.FloatField(required=True)
type = serializers.CharField(required=True)
volume = serializers.IntegerField(required=True)
just pass your BarBeer object to this serializer and it would return all the data points, even for the objects connected through Foreign Key.
Another way to achieve this as the exact same response that you mentioned in the question would be to create a renderer for you api and format and structure the data as you want in it accordingly.