blocks|key|1815868|text|您关注重复信息是正确的；数据库设计(特别是数据库规范化)的一个主要关注点是避免重复信息，从而消除不一致数据的可能性。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1815869|然而，在这种情况下，我认为将处方和配药分开更有意义。这是两件不同的事情，在现实世界中，很可能会犯错误，也很可能送错了药。虽然人们应该努力防止这样的错误，但这与不可能在数据模型中表示错误是截然不同的。|1815870|因此，我的建议是在应用程序层使用validate+the+data，而不是在数据模型本身中构建约束。类似于：|offset|length|1815871|class+ActiveIngredient(models.Model):
++++...

class+Medicine(models.Model):
++++quantity+=+models.IntegerField()
++++active_ingredient+=+models.ForeignKey("ActiveIngredient",+on_delete=models.CASCADE)

class+Person(models.Model):
++++...

class+Prescription(models.Model):
++++...
++++customer+=+models.ForeignKey("Person",+on_delete=models.CASCADE)
++++active_ingredient+=+models.ForeignKey("ActiveIngredient",+on_delete=models.CASCADE)
++++quantity+=+models.IntegerField()

class+PersonStock(models.Model):
++++prescription+=+models.ForeignKey("Prescription",+on_delete=models.CASCADE)
++++medicine+=+models.ForeignKey("Medicine",+on_delete=models.CASCADE)
++++expiration_date+=+models.DateField()

++++#+Make+sure+the+supplied+medicine+is+correct.
++++def+clean(self):
++++++++if+self.medicine.active_ingredient+!=+self.prescription.active_ingredient:
++++++++++++raise+ValidationError("Wrong+medicine!")|code-block|syntax|javascript|1815872|或者，您可以仅在创建PersonStock时进行检查。|style|CODE|1815873|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.djangoproject.com/en/dev/ref/models/instances/#django.db.models.Model.clean^0|0|0|G|H|0|0|0|A|B|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@$F|11|G|12|1|13]]|A|$]]|$1|H|3|I|5|J|7|14|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|15|8|@$F|16|G|17|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

You're right to be concerned about duplicated information; a major concern of database design (specifically database normalization) is avoiding that so as to eliminate the possibility of inconsistent data.

In this case, however, I think it makes more sense to keep prescriptions and their filling separate. These are two separate things, and in the real world it's very possible for mistakes to be made and the wrong medicine to be delivered. While one should endeavor to prevent such mistakes, that's very different from making it impossible to represent a mistake in your data model.

So my recommendation would be to <a href="https://docs.djangoproject.com/en/dev/ref/models/instances/#django.db.models.Model.clean" rel="nofollow noreferrer">validate the data</a> at the application layer rather than building constraints into the data model itself. Something like:

<pre><code>class ActiveIngredient(models.Model):
 ...

class Medicine(models.Model):
 quantity = models.IntegerField()
 active_ingredient = models.ForeignKey("ActiveIngredient", on_delete=models.CASCADE)

class Person(models.Model):
 ...

class Prescription(models.Model):
 ...
 customer = models.ForeignKey("Person", on_delete=models.CASCADE)
 active_ingredient = models.ForeignKey("ActiveIngredient", on_delete=models.CASCADE)
 quantity = models.IntegerField()

class PersonStock(models.Model):
 prescription = models.ForeignKey("Prescription", on_delete=models.CASCADE)
 medicine = models.ForeignKey("Medicine", on_delete=models.CASCADE)
 expiration_date = models.DateField()

 # Make sure the supplied medicine is correct.
 def clean(self):
 if self.medicine.active_ingredient != self.prescription.active_ingredient:
 raise ValidationError("Wrong medicine!")
</code></pre>

Alternatively you could do the check only when a <code>PersonStock</code> is being created.

I have a database design and relationships problem and I am concerned with possible circular references.

To give an example, Jack has on his stock Medicines A, B and C. Medicines A and B have an active_ingredient AI1 and medicine C has an active_ingredient AI2.

Jack goes to the doctor, who prescribes him AI1. For the Prescription object, it is indifferent if he takes Medicine A or B.

Here is an example code:

<pre><code>class ActiveIngredient(models.Model):
 ...

class Medicine(models.Model):
 quantity = models.IntegerField()
 active_ingredient = models.ForeignKey("ActiveIngredient", on_delete=models.CASCADE)

class Person(models.Model):
 ...

class PersonStock(models.Model):
 customer = models.ForeignKey("Person", on_delete=models.CASCADE)
 medicine = models.ForeignKey("Medicine", on_delete=models.CASCADE)
 expiration_date = models.DateField()

class Prescription(models.Model):
 ...
 quantity = models.IntegerField()
</code></pre>

What is the best solution to model this relationship?

Changing Prescription to this:

<pre><code>class Prescription(models.Model):
 ...
 customer = models.ForeignKey("Person", on_delete=models.CASCADE)
 active_ingredient = models.ForeignKey("ActiveIngredient", on_delete=models.CASCADE)
 quantity = models.IntegerField()
</code></pre>

Seems wrong to me given that there is the PersonStock class already connecting Person and Medicine.

django models - Avoid possible circular reference in database design

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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