Query set for many to many object relationship - django

Question

Need to post many items onetime -many titles- in a titles list from mobile app to the backend, the problem is when use create method within the for loop it gets no record in database & that Type Error -Direct assignment to the forward side of a many-to-many set is prohibited. Use container.set() instead.- when try to use the set() method it's not showing any right case!!!!, the problem is when to use create in order to made many create objects in many-to-many relationship. please guide.
models.py
class Container(models.Model):
name = models.CharField(max_length=200, blank=False)
capacity = models.IntegerField( null=False ,blank=False)
class Item(models.Model):
title = models.CharField(max_length=200, blank=False)
container = models.ManyToManyField(container)
serializers.py
class ContainerSerializer(serializers.ModelSerializer):
class Meta:
model = Container
fields = '__all__'
class ItemSerializer(serializers.ModelSerializer):
class Meta:
model = Item
fields = '__all__'
Request
{
"container": {
"name": "container1",
"capacity": 10,
},
"Items":[
{"title":"tl1",},
{"title":"tl2",},
{"title":"tl3",}
]
}
view.py
#api_view(['POST'])
def additems(request):
data = request.data
container = Container.objects.create(
name = data['name']
capacity = data['capacity']
)
container.save()
for i in Items:
item = Item.objects.create(
container = container ,
title = i['title'] ,
)
item.save()
serializer = ContainerSerializer(container, many=False)
return response(serializer.data)
TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use container.set() instead.
Why getting this error ?!!! please guide ...

Answer 1

The error is occurring because you are attempting to create and assign a Container object to a ManyToManyField on the Item model using the create() method within a for loop. This will result in a new container being created for each iteration of the loop, which is not what you want. Additionally, when attempting to add Item objects to a many-to-many relationship with a Container object, you should use the add() method, not the set() method. You can refactor your view like this
#api_view(['POST'])
def additems(request):
data = request.data
# Create the container
container = Container.objects.create(
name=data['container']['name'],
capacity=data['container']['capacity']
)
# Create the items and add them to the container
items = data['Items']
for item_data in items:
item = Item.objects.create(title=item_data['title'])
container.item_set.add(item)
serializer = ContainerSerializer(container)
return Response(serializer.data)
In the ContainerSerializer, you need to specify the ItemSerializer as a nested serializer in order to properly serialize the Item objects that are associated with the Container through the many-to-many relationship.As shown below:
class ContainerSerializer(serializers.ModelSerializer):
items = ItemSerializer(many=True, read_only=True)
class Meta:
model = Container
fields = ['id', 'name', 'capacity', 'items']