text: from django.db import models
  from user.models import User
  from chat.models import Response
  from chat import constants
  
  
  class Message(models.Model):
      """
      Create a Message model in database.
      """
  
      user_from = models.ForeignKey(User, related_name="user_from")
      user_to = models.ForeignKey(User, related_name="user_to")
  
      subject = models.CharField(max_length=constants.MAX_LENGTH_TEXT_SUBJECT)
      date = models.DateField(auto_now=True)
  
      is_active_patient = models.BooleanField(default=True)
      is_active_health_professional = models.BooleanField(default=True)
  
      # List of response in Message.
      messages = models.ManyToManyField(Response, default=None)
  