Filter queryset of django inline formset based on attribute of through model

Question

I have a basic restaurant inventory tracking app that allows the user to create ingredients, menus, and items on the menus. For each item on a given menu, the user can list the required ingredients for that item along with a quantity required per ingredient for that item.

Menu items have a many-to-many relationship with ingredients, and are connected via an "IngredientQuantity" through table.

Here are my models:

class Ingredient(models.Model):
    GRAM = 'Grams'
    OUNCE = 'Ounces'
    PIECE = 'Pieces'

    UNIT_CHOICES = [
        ('Grams', 'Grams'),
        ('Ounces', 'Ounces'),
        ('Pieces', 'Pieces')
    ]

    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, blank=True) 
    name = models.CharField(max_length=200)
    unitType = models.CharField(max_length=200, choices=UNIT_CHOICES, verbose_name='Unit')
    unitCost = models.DecimalField(max_digits=10, decimal_places=2, verbose_name='Unit Cost')
    inventoryQuantity = models.DecimalField(max_digits=10, decimal_places=2, verbose_name='Quantity')

    def __str__(self):
        return self.name + ' (' + self.unitType + ')'

    def totalCost(self):
        result = self.inventoryQuantity * self.unitCost
        return "{:.0f}".format(result)

class Menu(models.Model):
    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, blank=True) 
    name = models.CharField(max_length=200)
    timeCreated = models.DateTimeField(auto_now_add=True)
    timeUpdated = models.DateTimeField(auto_now=True)

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

class MenuItem(models.Model):
    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, blank=True)
    name = models.CharField(max_length=200)
    price = models.DecimalField(max_digits=10, decimal_places=2)
    ingredients = models.ManyToManyField(Ingredient, through='IngredientQuantity')
    menu = models.ForeignKey(Menu, on_delete=models.CASCADE, null=True)

    def __str__(self):
        return self.name

    def itemCost(self):
        relevantIngredients = IngredientQuantity.objects.filter(menuItem=self)
        cost = 0

        for ingredient in relevantIngredients:
            cost += (ingredient.ingredient.unitCost * ingredient.ingredientQuantity)

        return cost

class IngredientQuantity(models.Model):
    user = models.ForeignKey(User, on_delete=models.SET_NULL, null=True, blank=True) 
    ingredient = models.ForeignKey(Ingredient, on_delete=models.CASCADE)
    menuItem = models.ForeignKey(MenuItem, on_delete=models.CASCADE)
    ingredientQuantity = models.IntegerField(default=0)

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

This is a multi-user app, so when a user creates a new item on a menu and adds ingredients to it, they should only have the option of choosing ingredients they have created, not those of other users. Here is my attempt to do that in my views:

def ItemUpdate(request, pk):
    item = MenuItem.objects.get(id=pk)
    user = request.user

    IngredientQuantityFormset = inlineformset_factory(
        MenuItem, IngredientQuantity, fields=('ingredient', 'ingredientQuantity'), can_delete=True, extra=0
    )

    form = ItemCreateForm(instance=item)
    formset = IngredientQuantityFormset(instance=item, queryset=IngredientQuantity.objects.filter(ingredient__user=user))

    if request.method == 'POST':
        form = ItemCreateForm(request.POST, instance=item)
        formset = IngredientQuantityFormset(request.POST, instance=item, queryset=IngredientQuantity.objects.filter(ingredient__user=user))

# rest of view...

I've searched everywhere for how to implement the queryset parameter properly, but I cannot get it to work. When creating an item on a menu, the user still has the ability to choose from every ingredient in the database (including the ones created by other users). I would like the user to only be able to choose from the ingredients they themselves created.

Does anyone know how to do this properly? Thank you!

Answer 1

I received some guidance on Django forums and arrived at a solution which is documented below:

https://forum.djangoproject.com/t/filter-dropdown-options-in-django-inline-formset-based-on-attribute-of-through-model/13374/3