英文:
Creating a conditional Many to Many relation in Django
问题
看起来很容易，但我仍然不知道如何实现它。
尝试在三个模型之间创建多对多的条件关系（不确定是否是正确的命名方式！）：
Class Book(models.Model):book_name = models.CharField(max_length=50)Class Article(models.Model):article_name = models.CharField(max_length=50)Class Portfolio(models.Model):KINDS = [('B', 'Book'), ('A', 'Article')]book = models.ForeignKey(Book, on_delete=models.PROTECT)article = models.ForeignKey(Article, on_delete=models.PROTECT)kind = models.models.CharField(max_length=1, choices=KINDS)user = models.ManyToManyField(User, through='Recommendation')Class Recommendation(models.Model):user = models.ForeignKey(User, on_delete=models.PROTECT)portfolio = models.ForeignKey(Book, on_delete=models.PROTECT)date = models.DateTimeField()
英文:
It seems easy but I still can't figure out how to implement it.
Trying to create a Many to Many conditional relations (not sure if it's the correct way to name it!) between three models:
Class Book(models.Model):book_name = models.CharField(max_length=50)Class Article(models.Model):article_name = models.CharField(max_length=50)Class Portfolio(models.Model):KINDS = [('B', 'Book'), ('A', 'Article')]book = models.ForeignKey(Book, on_delete=models.PROTECT)article = models.ForeignKey(Article, on_delete=models.PROTECT)kind = models.models.CharField(max_length=1, choices=KINDS)user = models.ManyToManyField(User, through='Recommendation')Class Recommendation(models.Model):user = models.ForeignKey(User, on_delete=models.PROTECT)portfolio = models.ForeignKey(Book, on_delete=models.PROTECT)date = models.DateTimeField()
Each User (from the Django User module) can have multiple recommendations of portfolios. Each Portfolio is a group of books and articles recommended on a specific date.
答案1
得分: 2
我会跳过 Portfolio Model，直接这样实现：
class Book(models.Model):book_name = models.CharField(max_length=50)class Article(models.Model):article_name = models.CharField(max_length=50)class Recommendation(models.Model):user = models.ForeignKey(User, on_delete=models.PROTECT)book = models.ForeignKey(Book,blank=True,null=True,on_delete=models.PROTECT)article = models.ForeignKey(Article,blank=True,null=True,on_delete=models.PROTECT)date = models.DateTimeField()class Meta:constraints = [models.CheckConstraint(check=Q(book__isnull=True, article__isnull=False) | Q(book__isnull=False, article__isnull=True),name='only_book_or_article')]
你可以跳过约束，但这样可能会导致你的数据不一致。
英文:
I would skip the Portfolio Model and just implement it this way:
class Book(models.Model):book_name = models.CharField(max_length=50)class Article(models.Model):article_name = models.CharField(max_length=50)class Recommendation(models.Model):user = models.ForeignKey(User, on_delete=models.PROTECT)book = models.ForeignKey(Book,blank=True,null=True,on_delete=models.PROTECT)article = models.ForeignKey(Article,blank=True,null=True,on_delete=models.PROTECT)date = models.DateTimeField()class Meta:constraints = [models.CheckConstraint(check=Q(book__isnull=True, article__isnull=False) | Q(book__isnull=False, article__isnull=True),name='only_book_or_article')]
you could skip the constrains but than you risk that your data is inconsistent
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