如何将属性添加到 python class 中的实例变量

Question

To keep this simple, in my Django/Python sports pool application, each user is creating their own pool. Therefore, in the Pool class, I need to make all the class variables be instance variables so no user is changing values on another users Pool class instance.

A quick sample of code in the models.py file would be:

  class Pool(models.Model):
     def __init__(self, team_name):
         self.team_name = team_name

What if I wanted to add attributes to the team_name field such as max_length = 100 or unique=True

I understand the instance variables values must be passed to the class upon instantiation, so is it that the value being passed must already be defined with those attributes? How do I handle this. Thanks!

ps My apologies if I screwed up the formatting of this question. I'm having challenges with inserting code. Sorry!

Answer 1

You can just add it into the field, for example:

class Pool(models.Model): 
    team_name = models.CharField(max_length=100, unique=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE)

And so on. You can refer to the documentation: https://docs.djangoproject.com/en/3.0/ref/models/fields/

Adding a unique constraint: https://docs.djangoproject.com/en/3.0/ref/models/constraints/#uniqueconstraint

Answer 2

If I understand what you are saying, you don't have to pass the variables on instantiation if the fields are blank=True and null=True . You can then override the save() method to make sure they are there before committing to the database.

For instance in models.py:

class Pool(models.Model):
    name = models.CharField(max_length=100, unique=True, blank=True, null=True)
    user = models.ForeignKey(User, on_delete=models.CASCADE, blank=True, null=True)

    def save(self, *args, **kwargs): 
        if self.name is None or self.user is None:
            raise ValueError # or do something else or raise another error
        else:
            super(Pool, self).save(*args, **kwargs) 

In your views.py:

def pools(request):
    ...
    try:
        user1_pool = Pool.objects.create()
        user1_pool.name = "My Pool Name"
        user1_pool.user = request.user
        user1_pool.save()
    except ValueError:
        # do something, send a message to user, etc.
    ...
    try:
        user2_pool = Pool.objects.create()
        user2_pool.name = "Another Pool Name"
        user2_pool.user = some_other_user
        user2_pool.save()
    except ValueError:
        # do something, send a message to user, etc.
    ...