具有Model方法的Django queryset包含另一个queryset [英] Django queryset with Model method containing another queryset

问题描述

假设我有一个模型 MyModel ，该模型具有使用另一模型的查询集的属性方法.

  class OtherModel(models.Model)...类MyModel(models.Model):simple_attr = models.CharField('Yada yada')@财产def complex_attr():list_other_model = OtherModel.objects.all()...#使用来自'OtherModel'和simple_attr的queryset的复杂算法返回结果 

这将导致我在 MyModel 上的 get_queryset()方法查询数据库以每次为每一行生成 list_other_model 变量./p>

这导致我的MyModel ListView 生成数百个SQL查询.效率不高.

当使用 MyModel.objects.all()时，如何构造Manager或get_queryset方法为每行缓存变量 list_other_model ?

我希望我的问题是有道理的-我正在尝试第六杯意式浓缩咖啡，但仍然没有找到减少db查询的方法.

解决方案

不确定这是否是最好的方法，但是可以.

如果有人发布更好的答案，我会接受他们的答案.

  class OtherModel(models.Model)...类MyModelManager(models.Manager):def get_queryset(self):self.model.list_other_model = OtherModel.objects.all()返回super(MyModelManager，self).get_queryset()类MyModel(models.Model):simple_attr = models.CharField('Yada yada')list_other_model =无对象= MyModelManager()@财产def complex_attr():...#使用来自'OtherModel'和simple_attr的queryset的复杂算法返回结果 

Suppose I have a model, MyModel, with a property method that uses another model's queryset.

class OtherModel(models.Model)
    ...

class MyModel(models.Model):
    simple_attr = models.CharField('Yada yada')

    @property
    def complex_attr(self):
        list_other_model = OtherModel.objects.all()
        ...
        # Complex algorithm using queryset from 'OtherModel' and simple_attr
        return result

This causes my get_queryset() method on MyModel to query the database to generate the list_other_model variable every time for every single row.

Which causes my MyModel ListView to generate hundreds of SQL queries. Not efficient.

How can I architect a Manager or get_queryset method to cache the variable list_other_model for each row when using MyModel.objects.all()?

I hope my question makes sense--I'm on my sixth shot of espresso, and still haven't found a way to reduce the db queries.

解决方案

Not sure if this is the best way to do it, but it works.

If someone posts a better answer, I'll accept theirs.

class OtherModel(models.Model)
    ...

class MyModelManager(models.Manager):
    def get_queryset(self):
        self.model.list_other_model = OtherModel.objects.all()
        return super(MyModelManager, self).get_queryset()

class MyModel(models.Model):
    simple_attr = models.CharField('Yada yada')
    list_other_model = None

    objects = MyModelManager()

    @property
    def complex_attr(self):
        ...
        # Complex algorithm using queryset from 'OtherModel' and simple_attr
        return result

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