我有这样的模型：
```python
class Location(models.Model):
    pass
class Place(Location):
    name = models.CharField(...)
    def __str__(self):
        return str(self.name)
class Coordinates(Location):
    x = models.DecimalField(...)
    y = models.DecimalField(...)
    def __str__(self):
        return f"({x}, {y})"

<details>
<summary>英文:</summary>
I have such models:

def __str__(self):
    return str(self.name)

def __str__(self):
    return f"({x}, {y})"

If I try to query ```Location.objects.get(pk=1).__str__()```, I get ```Location object (1)```, instead I expect ```(123, 456)```.
How can I make objects to use their own ```__str__()``` method, instead of model's through which I've accessed the object?
</details>
# 答案1
**得分**: 0
如果我尝试查询 `Location.objects.get(pk=1)`，我会得到 `&lt;Location object (1)&gt;`，而我期望得到 `(123, 456)`。
Django 不会自动降级，这可能是出于性能原因：它需要对`Place`和`Coordinates`两个表进行`LEFT OUTER JOIN`操作，以确定是哪一个，然后进行一些魔法操作来创建一个`Coordinate`模型。随着子类的增多（包括子子类等），连接操作的数量将会变得庞大，会对性能造成严重的影响。
如果你真的需要这个功能，有一些像 [**`django-polymorphic`**&amp;nbsp;&lt;sup&gt;\[readthedocs\]&lt;/sup&gt;](https://django-polymorphic.readthedocs.io/en/stable/) 这样的包可以实现上面描述的流程，但总的来说，关系数据库不太适合处理继承，因此模型继承通常不是一个好主意。
<details>
<summary>英文:</summary>
&gt; If I try to query `Location.objects.get(pk=1)`, I get `&lt;Location object (1)&gt;`, instead I expect `(123, 456)`.
Django does not automatically downcast, likely for performance reasons: it would mean it has to make `LEFT OUTER JOIN`s to the tables of both `Place` and `Coordinates`, to see which one it is, and then do some magic to create a `Coordinate` model instead. As the number of subclasses grows (including grandchildren, etc.), the amount of `JOIN`s will become huge, with a severe performance penalty.
If you really want this, there are packages like [**`django-polymorphic`**&amp;nbsp;&lt;sup&gt;\[readthedocs\]&lt;/sup&gt;](https://django-polymorphic.readthedocs.io/en/stable/) that implement the flow described above, but in general relational databases are just not good with inheritance, and therefore model inheritance is often not a good idea anyway.
</details>