chat structure

class Ticket(models.Model):
    id = models.AutoField(primary_key=True)
    ticket_priority = models.ForeignKey(TicketPriority, models.SET_NULL, db_column='ticket_priority', blank=False, null=True)
    ticket_subject = models.CharField(max_length=300, blank=False, null=False)
    ticket_description = models.CharField(max_length=1000, blank=True, null=False)
    created_at_dtm = models.DateTimeField(auto_now_add=True)
    closed_at_dtm = models.DateTimeField(blank=True, null=True)
    answered_at_dtm = models.DateTimeField(blank=True, null=True)
    ticket_type = models.ForeignKey(TicketType, models.SET_NULL, db_column='ticket_type', blank=False, null=True)
    ticket_status = models.ForeignKey(TicketStatus, models.SET_NULL, db_column='ticket_status', blank=False, null=True)
    request_id = models.ForeignKey(Request, models.CASCADE, blank=False, null=False)
    creator = models.ForeignKey(Employee, models.SET_NULL, db_column="ticket_creator", related_name="created_tickets",blank=False, null=True)
    tech_sup_responder = models.ForeignKey(Employee, models.SET_NULL, related_name="responded_tickets",blank=False, null=True)



class Discussion(models.Model):
    id = models.AutoField(primary_key=True)
    ticket = models.ForeignKey(Ticket, models.CASCADE, blank=False, null=False)
    created_at_dtm = models.DateTimeField(blank=False, null=False)


class Message(models.Model):
    id = models.AutoField(primary_key=True)
    discussion = models.ForeignKey(Discussion, models.CASCADE, blank=False, null=False)
    employee = models.ForeignKey(Employee, models.SET_NULL, blank=False, null=True)
    message_text = models.CharField(max_length=500, blank=True, null=False)
    created_at_dtm = models.DateTimeField(auto_now_add=True)


class Employee(models.Model):
    id = models.AutoField(primary_key=True)
    password = models.CharField(max_length=300, blank=False, null=False)
    login = models.CharField(max_length=100, blank=False, null=False)
    full_name = models.CharField(max_length=100, blank=False, null=False)
    employee_role = models.ForeignKey(EmployeeRole, models.DO_NOTHING, db_column='employee_role', blank=False, null=True)