Untitled

class ShoppingCart(models.Model):
    user = models.OneToOneField(
        User, verbose_name='User', on_delete=models.CASCADE,
        related_name='shopping_cart',
    )
    recipes = models.ManyToManyField(
        Recipe, verbose_name='Ingredients', through='ShoppingCartRecipe',
        related_name='shopping_cart',
    )

    class Meta:
        verbose_name = 'Список покупок'
        verbose_name_plural = 'Списки покупок'
        constraints = [
            models.UniqueConstraint(
                fields=['user'],
                name='only one shopping cart for user',
            ),
        ]

    def get_recipes(self):
        return "\n".join([i.name for i in self.recipes.all()])

    def __str__(self):
        return f'{self.user}\' shopping cart'


class ShoppingCartRecipe(models.Model):
    shopping_cart = models.ForeignKey(
        ShoppingCart, on_delete=models.CASCADE,
        related_name='shopping_cart_recipe',
    )
    recipe = models.ForeignKey(
        Recipe, on_delete=models.CASCADE, related_name='shopping_cart_recipe',
    )

    class Meta:
        verbose_name = 'Рецепт в списке покупок'
        verbose_name_plural = 'Рецепты в списке покупок'

    def __str__(self):
        return f'{self.recipe} in {self.shopping_cart}'