Unique ManyToManyField DRF - django

Question

I do not want to be able to create multiple Chat objects with the same EXACT participants field.
For example:
If a chat already exists, with participants=["user1", "user2"],
I do not want to be able to create a new chat objects with the same EXACT participants
Looking for something like unique=True, except for manytomanyfield.
Models:
class Contact(models.Model):
user = models.ForeignKey(
User, related_name='friends', on_delete=models.CASCADE)
friends = models.ManyToManyField('self', blank=True)
def __str__(self):
return self.user.username
class Message(models.Model):
contact = models.ForeignKey(
Contact, related_name="messages", on_delete=models.CASCADE)
content = models.TextField()
timestamp = models.DateTimeField(auto_now_add=True)
def __str__(self):
return self.contact.user.username
class Chat(models.Model):
participants = models.ManyToManyField(
Contact, related_name='chats')
messages = models.ManyToManyField(Message, blank=True)
def __str__(self):
return f"{self.pk}"
Serializer:
class ContactSerializer(serializers.StringRelatedField):
def to_internal_value(self, value):
return value
class ChatSerializer(serializers.ModelSerializer):
participants = ContactSerializer(many=True)
class Meta:
model = Chat
fields = ("id", "messages", "participants")
read_only = ('id')
def create(self, validated_data):
print(validated_data)
participants = validated_data.pop('participants')
# for c in Chat.participant_set.all():
# print(c)
chat = Chat()
chat.save()
for username in participants:
contact = get_user_contact(username)
chat.participants.add(contact)
chat.save()
return chat

Answer 1

Probably you can try like this:
participants = validated_data.pop('participants')
prev_chat = Chat.objects.all()
for username in participants:
prev_chat = prev_chat.filter(participants__username=username)
if prev_chat.exists():
chat = prev_chat.first()
else:
chat = Chat()
chat.save()
for username in participants:
contact = get_user_contact(username)
chat.participants.add(contact)