如何在 Django 中使用以下关系约束 model 注册系统？

Question

I am trying to create a hackathon management system web application using Django. Each hackathon can have as many participating universities as possible (No constraints here).Now, each participating university can have at most 3 teams and each team can have at most 4 persons (1-4). I'm new to Django so help would be much appreciated.

from django.db import models


class Hackathon(models.Model):
    name = models.CharField(max_length=50,blank=True,default='')
    eventId = models.CharField(max_length=50, blank=True, default='')
    startDate = models.DateField(null=True)
    endDate = models.DateField(null=True)
    location = models.TextField(max_length=100, blank=True, default='')
    description = models.TextField(max_length=800, blank=True, default='')
    #participants = models.ManyToManyField(...)??

    def __str__(self):
        return self.name

class University(models.Model):
    name = models.CharField(max_length=50)

    def __str__(self):
        return self.name


class Team(models.Model):
    team_name = models.CharField(max_length=50)
    member_count = models.PositiveIntegerField(default=1, validators=[MinValueValidator(1), MaxValueValidator(4)])
    uni = models.ForeignKey(University, on_delete = models.CASCADE)

    def __str__(self):
        return self.team_name

class Person(models.Model):
    name = models.CharField(max_length=50)
    belongs_to = models.ForeignKey(Team,on_delete = models.CASCADE)

Answer 1

Your relational schema seems right for the use-case you describe.

The constraints you describe ( at most 3 teams and each team can have at most 4 persons ) are not really DB constraints but rather application constraints . You will probably have to define a validation logic in overriding your Models save() method.

class Team(models.Model):

  def save(self, *args, **kwargs):
    if self.uni.teams.count() >= 3:
      raise ValidationError("This university already has its 3 teams")
    super().save(*args, **kwargs)



class Person(models.Model):

  def save(self, *args, **kwargs):
    if self.team.persons.count() >= 4:
      raise ValidationError("This team already has its 4 people")
    super().save(*args, **kwargs)

Also, I would recommend you to use Django 'User' model , which comes with several utils: password management, username unicity, ...etc.