ListField in serializer giving 'ManyRelatedManager' object is not iterable error

[Arjun Nambiar]

models.py

class IP(models.Model):
name = models.CharField(max_length=30, unique=True)
address = models.CharField(max_length=50, unique=True)

class IPGroup(models.Model):
name = models.CharField(max_length=50, unique=True)
ips = models.ManyToManyField('IP', through='IPGroupToIP')

class IPGroupToIP(models.Model):
ip_group = models.ForeignKey('IPGroup', on_delete=models.CASCADE)
ip = models.ForeignKey('IP', on_delete=models.CASCADE)


serializers.py

class IPGroupCreateSerializer(serializers.ModelSerializer):
ips = serializers.ListField()
class Meta:
model = IPGroup
fields = ['name', 'ips']

@transaction.atomic()
def create(self, validated_data):
ips_data = validated_data.pop('ips', None)
ip_group = IPGroup.objects.create(name=validated_data['name'])
if ips_data:
for ip in ips_data:
ip_obj, created = IP.objects.get_or_create(name=ip['name'], address=ip['address'])
IPGroupToIP.objects.create(ip_group_id=ip_group.id, ip_id=ip_obj.id)
return ip_group


views.py

class IPGroupCreateView(generics.CreateAPIView):
queryset = IPGroup.objects.get_queryset()
serializer_class = IPGroupCreateSerializer


JSON payload

{ "ips": [{"name":"example.com", "address":"10.1.1.9"}], "name": "ipgroup1" }


Expected behavior

{"name": "ipgroup1", "ips": [{"name": "example.com", "address": "10.1.1.9"}]}


Actual behavior


*TypeError at /api/v1/ip-group/'ManyRelatedManager' object is not iterable*



This strangely works if i set write_only=True to the ListField but then the
**ips** fiels is not available in the serializer response data. I went
through the documentation and did not see this behavior mentioned anywhere.
What am I doing wrong ?

[Arjun Nambiar]

The strange thing is that when i check the DB it actually created
everything..the object and the M2M relationships..Just that it is not able
to give a 201 Respone back

Post by Arjun Nambiar
models.py
name = models.CharField(max_length=30, unique=True)
address = models.CharField(max_length=50, unique=True)
name = models.CharField(max_length=50, unique=True)
ips = models.ManyToManyField('IP', through='IPGroupToIP')
ip_group = models.ForeignKey('IPGroup', on_delete=models.CASCADE)
ip = models.ForeignKey('IP', on_delete=models.CASCADE)
serializers.py
ips = serializers.ListField()
model = IPGroup
fields = ['name', 'ips']
@transaction.atomic()
ips_data = validated_data.pop('ips', None)
ip_group = IPGroup.objects.create(name=validated_data['name'])
ip_obj, created = IP.objects.get_or_create(name=ip['name'], address=ip['address'])
IPGroupToIP.objects.create(ip_group_id=ip_group.id, ip_id=ip_obj.id)
return ip_group
views.py
queryset = IPGroup.objects.get_queryset()
serializer_class = IPGroupCreateSerializer
JSON payload
{ "ips": [{"name":"example.com", "address":"10.1.1.9"}], "name": "ipgroup1" }
Expected behavior
{"name": "ipgroup1", "ips": [{"name": "example.com", "address": "10.1.1.9"}]}
Actual behavior
*TypeError at /api/v1/ip-group/'ManyRelatedManager' object is not iterable*
This strangely works if i set write_only=True to the ListField but then
the **ips** fiels is not available in the serializer response data. I went
through the documentation and did not see this behavior mentioned anywhere.
What am I doing wrong ?

[Dipen bhatt]

Well, the objects are definitely getting created in the database. But when
DRF is trying to send the output it tries to deserialize the objects in the
to_representation function, but as you are using a list field it simply
cannot deserialize as many to many relationship , since it returns a
manager and not a iterable.
Thats why you are getting a error.


Maybe one way to run your code using List Field, is to override the
to_representation function and manually add the IPs to the attribute.
But this is gonna be too much hassle and your code may become ugly.

[cbertinato via Django REST framework]

You don't need to use a ListField if you're not going to validate, and by
not passing a child parameter you are indeed not validating the items in
the list.

http://www.django-rest-framework.org/api-guide/fields/#listfield

If all you want to do is return the list of things in the many-to-many, you
don't need to explicitly specify the field in a model serializer. You can,
however, use a nested a serializer, which is probably more appropriate in
this case:

class IPGroupCreateSerializer(serializers.ModelSerializer):
ips = IPSerializer(read_only=True, many=True)

If you want to used the nested serializer for deserialization as well, then
you will need to also implemented an update method in your
IPGroupCreateSerializer.

http://www.django-rest-framework.org/api-guide/relations/#writable-nested-serializers

[Arjun Nambiar]

I did not post it here to make the code more complex but I am performing
some validations.I understand that it works with the Nested serializers but
I need to understand what am I doing wrong that it is not working with a
ListField

On Thursday, 27 September 2018 18:14:59 UTC+5:30,

Post by cbertinato via Django REST framework
You don't need to use a ListField if you're not going to validate, and by
not passing a child parameter you are indeed not validating the items in
the list.
http://www.django-rest-framework.org/api-guide/fields/#listfield
If all you want to do is return the list of things in the many-to-many,
you don't need to explicitly specify the field in a model serializer. You
can, however, use a nested a serializer, which is probably more appropriate
ips = IPSerializer(read_only=True, many=True)
If you want to used the nested serializer for deserialization as well,
then you will need to also implemented an update method in your
IPGroupCreateSerializer.
http://www.django-rest-framework.org/api-guide/relations/#writable-nested-serializers