筛选中介ManyToMany django [英] Filter intermediary ManyToMany django

问题描述

class Ingredient(Model):
    name = CharField(max_length=55, unique=True)

    def __str__(self):
        return self.name

    class Meta:
        ordering = ('name',)



class Product(Model):
    name = CharField(max_length=55)

    def __str__(self):
        return self.name

    class Meta:
        ordering = ('name', )


class ProductIngredient(Model):
    product = ForeignKey(Product, on_delete=CASCADE, related_name='product_ingredients')
    ingredient = ForeignKey(Ingredient, on_delete=CASCADE)
    optional = BooleanField(default=False)

    class Meta:
        unique_together = (('product', 'ingredient'),)
        ordering = ('product__name',)

    def __str__(self):
        return f'{self.product} - {self.ingredient}'

我要进行两个查询：

• sele ct所有成分包含草莓和牛奶的产品


• 选择所有成分包含草莓或牛奶的产品

第一个查询是： Product.objects.prefetch_related（'product_ingredients__ingredient'）。filter（product__ingredients__ingredient__name ='strawberry'）。filter（product__ingredients__ingredient__name ='milk'）

我需要在第一个查询中写 distinct 吗？
如何编写第二个查询？

Do I need to write distinct in the first query? How to write the second query?

推荐答案

Do I need to write distinct in the first query?

否，或者如果 product -成分的组合是唯一的，例如此处。这将是截然不同的，因为两种成分是截然不同的。此外，除非您确实要使用相关的呈现 Product ，否则您不应在此处使用 .prefetch_related（..） 成分 s。这样就足够了：

No, or at least not if the product-ingredient combination is unique, like here. It will be distinct, since the two ingredients are clearly distinct. You furthermore should not use .prefetch_related(..) here, unless you really want to render the Product with the related Ingredients. So it is sufficient to write:

Product.objects.filter(
    product__ingredients__ingredient__name='strawberry'
).filter(
    product__ingredients__ingredient__name='milk'
)

如何编写第二个查询？

How to write the second query?

您可以使用> __ in 查找[Django-doc] ：

Product.objects.filter(
    product__ingredients__ingredient__name__in=['strawberry', 'milk']
)

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