django restframework - Serializer for creating m2m relationship

Question

I am using django-restframework for my API. I created a serializer which should list my objects and should be able to create them.

I have a Contact entity and Product. There is a standard m2m between it for the likes.

Here's my model:

class Contact(models.Model):
    ...
    products_of_interest = models.ManyToManyField(Product, related_name="interested_contacts")

My serializer is as simple as it gets:

class ContactSerializer(serializers.ModelSerializer):

    class Meta:
        model = Contact

When I list my contacts via this serializer I get all my contact objects with an array of product ids - awesome:

"products_of_interest": [
        1,
        2
    ]

Now, when I want to create a contacts and populate the m2m, I get the following (via my Chrome Postman and form-data):

• Send products_of_interest = 1 --> works (!!!) but just for one product!
• Send products_of_interest = [1,2] --> needs pk and not unicode
• Send products_of_interest = 1;2 --> needs pk and not unicode
• Send products_of_interest[0] = 1, products_of_interest[1] = 2 --> nothing is done at all

I have some experience with serializers, so I thought, maybe I need to tell the serializer, that I want to give him more than one product. So I added this in my serializer:

products_of_interest = ProductSerializer(many=True, required=False, read_only=False)

Now I get this error:

"<Contact: >" needs to have a value for field "contact" before this many-to-many relationship can be used.

I'm totally lost now. What can I do? It can't be that I need to override standard rfw-functions for saving a damn easy m2m, can it?

Thanks!

Ron

Answer 1

What version of Django and drf are you using? I cannot reproduce your errors using Django 1.7 and drf 2.4.2. Here's my code:

models.py

from django.db import models

class Product(models.Model):
    pass


class Contact(models.Model):
    products_of_interest = models.ManyToManyField(Product,
        related_name="interested_contacts")

serializers.py

from .models import Contact
from rest_framework import serializers


class ContactSerializer(serializers.ModelSerializer):
    class Meta:
        model = Contact

views.py

from rest_framework import viewsets
from .models import Contact
from .serializers import ContactSerializer

class ContactViewSet(viewsets.ModelViewSet):
    queryset = Contact.objects.all()
    serializer_class = ContactSerializer

urls.py

from django.conf.urls import include, url

from rest_framework import routers
from . import views

router = routers.DefaultRouter()
router.register(r'contacts', views.ContactViewSet, 'contacts')
urlpatterns = router.urls

urlpatterns = [
    url(r'^', include(router.urls)),
    url(r'^api-auth/', include('rest_framework.urls', namespace='rest_framework'))
]

./manage.py shell
>>> from m2m_test.models import Product
>>> for i in range(3): Product.objects.create()
...
<Product: Product object>
<Product: Product object>
<Product: Product object>
>>>

And then in the web frontend at http://localhost:8000/contacts/:

POST with Raw Data form: { "products_of_interest": [1, 2, 3] }

-> just works.