Django-Rest-Framework POST request to ManyToMany Field - django

Question

I have a django model that is a message. It has a name which is a CharField, then also an array of users which is a ManyToManyField.
So This is what my API looks like:
[
{
"id": 13,
"content": "hej",
"date": "2019-07-09",
"sender": {
"id": 1,
"username": "william"
}
},
{
"id": 14,
"content": "hej william",
"date": "2019-07-09",
"sender": {
"id": 3,
"username": "ryan"
}
}
]
What I've tried to send via postman POST:
{
"content": "Hello",
"sender": {"username": "william"},
"date": "2019-09-02"
}
The Error I get:
sqlite3.IntegrityError: NOT NULL constraint failed: chat_message.sender_id
ManyToManyField(Userprofile=User):
class Message(models.Model):
sender = models.ForeignKey(UserProfile, on_delete=models.CASCADE, related_name="sendermessage")
content = models.CharField(max_length=500)
date = models.DateField(default=date.today)
canview = models.ManyToManyField(UserProfile, blank=True, related_name="messagecanview")
class Meta:
verbose_name_plural = 'Messages'
def __str__(self):
return "{sender}".format(sender=self.sender)

Answer 1

Assuming that you have a MessageSerializer class implemented, you could override its create() method in order to support writable nested representations:
class MessageSerializer(serializers.ModelSerializer):
...
def create(self, validated_data):
sender_data = validated_data.pop('sender')
sender = UserProfile.objects.create(**sender_data)
return Message.objects.create(sender=sender, **validated_data)
You pop the sender data from the dictionary, create a UserProfile instance with the attributes in there and then attach it to your Message creation.
This will resolve your error since now there is a real sender created before the actual message has been saved.