django-如何仅允许使用独立的数量重复数量？

发布于 2025-02-04 17:37:04 字数 1057 浏览 1 评论 0原文

我正在制作一个网页 - 一个可以租用电影，音乐CD和书籍的租赁场所。我已经创建了一个CD模型 -

class Cd(models.Model):
cd_band=models.CharField(max_length=100)
cd_title=models.CharField(max_length=100)
CD_GENRE= (
    ('POP', "POP"),
    ("HIP", "Hip-Hop"),
    ("ROC", "Rock"),
    ("BLU", "Blues"),
    ("SOU", "Soul"),
    ("COU", "Country"),
    ("JAZ", "Jazz"),
    ("CLA", "Classical music"),
)
cd_genre=models.CharField(max_length=3, choices=CD_GENRE)

cd_length=models.DurationField()

cd_rental=models.ForeignKey(Rental, on_delete=models.CASCADE, default=1)


def __str__(self):
       # return self.cd_title, '\n', self.cd_band, '\n'
        return "{} {} {}".format(self.cd_band,self.cd_title,self.cd_genre)

但是我必须在这里应用一条规则：

- 一个乐队可以在多达2种流派中提供CD。因此，假设我创建了Band1 -band1的CD，只能在2种流派中使用CD -Fe Rock and Blues。我不知道如何实施。我正在考虑制定一个约束，但我不知道要实现哪种条件：

UniqueConstraint.condition(fields=['cd_band','cd_genre'],condition=??????, name='unique_cd')

我还考虑过重组整个数据库 - 为乐队和音乐流派组成单独的类，然后将其与外国钥匙链接，设置向上验证器。我认为它应该可以工作，但是我必须做很多工作。还有其他方法吗？

原文

I'm making a webpage - a rental place that can rent movies, music cd's and books.
I've created a model of cd -

class Cd(models.Model):
cd_band=models.CharField(max_length=100)
cd_title=models.CharField(max_length=100)
CD_GENRE= (
    ('POP', "POP"),
    ("HIP", "Hip-Hop"),
    ("ROC", "Rock"),
    ("BLU", "Blues"),
    ("SOU", "Soul"),
    ("COU", "Country"),
    ("JAZ", "Jazz"),
    ("CLA", "Classical music"),
)
cd_genre=models.CharField(max_length=3, choices=CD_GENRE)

cd_length=models.DurationField()

cd_rental=models.ForeignKey(Rental, on_delete=models.CASCADE, default=1)


def __str__(self):
       # return self.cd_title, '\n', self.cd_band, '\n'
        return "{} {} {}".format(self.cd_band,self.cd_title,self.cd_genre)

But there is a rule that I have to apply here:

-One band can offer cd's in up to 2 genres. So let's say I create a cd of Band1 - Band1 can have cd's in only 2 genres - f.e rock and blues. I have no idea how to implement that.
I'm thinking about making a constraint, but I don't know what condition to implement:

UniqueConstraint.condition(fields=['cd_band','cd_genre'],condition=??????, name='unique_cd')

I've also thought of restructurizing my entire database - making a separate classes for bands and music genres, and then linking it with foreign keys, setting up validators. I think it should work, but I'd have to put in so much work.
Is there any other way of doing it?

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你的心境我的脸 2025-02-11 17:37:04

如果您想以这种方式构造数据库，那么IMO并不适合操纵和未来功能。我将支票放入save（）方法中。类似的内容：

def save(self, *args, **kwargs):
    bands_genres = set(Cd.objects.filter(cd_band=self.cd_band).values_list("cd_genre", flat=True))
    bands_genres.add(self.cd_genre)
    if len(bands_genres) > 2:
        raise SomeException
    super().save(*args, **kwargs)

*编辑：忘记添加通常您要在.distinct（） valice_list（）之后使用.distinct（），但是当我选择使用set时（）此解决方案。它不需要，并且具有与Difinse（）相同的效果。

If you want to have the database structured this way, which is IMO not great for manipulation and future features. I'd put the check into save() method. Something like this:

def save(self, *args, **kwargs):
    bands_genres = set(Cd.objects.filter(cd_band=self.cd_band).values_list("cd_genre", flat=True))
    bands_genres.add(self.cd_genre)
    if len(bands_genres) > 2:
        raise SomeException
    super().save(*args, **kwargs)

*Edit: Forgot to add that usually you want to use .distinct() after values_list(), but as I chose to use set() for this solution. It is not needed and has the same effect as distinct().

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