title: How to catch an error of creating chat room with two similar users?
body: <p>I am trying to create chat room instance in database. I need to catch an error when room with two similar users is creating.
  Here is my chat-room models.py:</p>
  <pre><code>class UserRoom(models.Model):
      class Meta:
          unique_together = ('user_one', 'user_two')
  
      room_id = models.UUIDField(default=uuid.uuid4, primary_key=True)
      user_one = models.ForeignKey('user.User', models.CASCADE, related_name='rooms_one')
      user_two = models.ForeignKey('user.User', models.CASCADE, related_name='rooms_two')
  
      def __str__(self):
          return f'{self.user_one} | {self.user_two} - {self.room_id}'
  </code></pre>
  <p>serializer.py:</p>
  <pre><code>def create(self, validated_data):
      user_one = self.context.get('request').user
      user_two = validated_data['user_two']
      
      room = UserRoom.objects.create(user_one=user_one, user_two=user_two)
      message = ChatMessage.objects.create(
          chat_room=room,
          sender=user_one,
          text=validated_data['message']
      )
      return room
  </code></pre>
  <p>views.py:</p>
  <pre><code>@action(methods=['POST'], detail=False)
  def create_chat(self, request):
      serializer = CreateChatSerializer(data=request.data,
                                         context=self.get_serializer_context())
      serializer.is_valid(raise_exception=True)
      a = serializer.save()
      return Response(
          UserRoomsSerializer(a, context=self.get_serializer_context()).data
      )
  </code></pre>
  <p>Also, I need an exception of creating existing room.</p>