python - Django Rest Framework writable nested serializers

Question

I'm writing a recipe organizer as a sample project for a class. I'm not very experienced with DRF other than using some very basic functionality. Here's the objective:

Create a new Recipe with associated Ingredients. Create the Ingredient objects at the same time as creating the Recipe object.

models.py:

class Ingredient(models.Model):
    name = models.CharField(max_length=100)

    def __str__(self):
        return self.name


class Recipe(models.Model):
    name = models.CharField(max_length=100)
    description = models.TextField(blank=True, null=True, help_text="This is a quick description of your recipe")
    directions = models.TextField(help_text="How to make the recipe")
    ingredients = models.ManyToManyField(Ingredient)

    def __str__(self):
        return self.name

serializers.py

class IngredientSerializer(serializers.ModelSerializer):

    class Meta:
        model = Ingredient


class RecipeSerializer(serializers.ModelSerializer):
    ingredients = IngredientSerializer(many=True)

    class Meta:
        model = Recipe

    def create(self, validated_data):
        ingredients_data = validated_data.pop('ingredients')
        recipe = Recipe.objects.create(**validated_data)
        for ingredient_data in ingredients_data:
            Ingredient.objects.create(**ingredient_data)
        return recipe

This successfully creates the Recipe object AND the Ingredients objects in the database, but doesn't associate the list of Ingredients with the Recipe. I assume this is because when I run ingredients_data = validated_data.pop('ingredients'), the validated_data dictionary gets its Ingredients removed, so when I create a new Recipe using validated_data, there aren't associated ingredients.

However I can't seem to figure out a way to keep ingredients associated with the recipe.

Answer 1

I figured out that ManyToMany relationships can't be established until all of the uncreated objects have been created. (See the Django Docs page on many-to-many relationships.)

Here's the working code:

serializers.py

class RecipeSerializer(serializers.ModelSerializer):
    ingredients = IngredientSerializer(many=True)

    class Meta:
        model = Recipe

    def create(self, validated_data):
        ingredients_data = validated_data.pop('ingredients')
        recipe = Recipe.objects.create(**validated_data)

        for ingredient in ingredients_data:
            ingredient, created = Ingredient.objects.get_or_create(name=ingredient['name'])
            recipe.ingredients.add(ingredient)
        return recipe

UPDATE:

Per request of @StevePiercy, below is my update() code. However, I haven't looked at this in years and have no idea whatsoever if it is correct or good. I haven't been working in Python or Django for some time now, so take this with a grain of salt:

def update(self, instance, validated_data):
    ingredients_data = validated_data.pop('ingredients')

    instance.name = validated_data.get('name', instance.name)
    instance.description = validated_data.get('description', instance.description)
    instance.directions = validated_data.get('directions', instance.directions)
    instance.photo = validated_data.get('photo', instance.photo)

    ingredients_list = []

    for ingredient in ingredients_data:
        ingredient, created = Ingredient.objects.get_or_create(name=ingredient["name"])
        ingredients_list.append(ingredient)

    instance.ingredients = ingredients_list
    instance.save()
    return instance