CODEWITHSUNDEEP
djangodjango-rest-framework
user8795870
user8795870

Reputation: 63

Django REST Framework: direct assignment to the forward side of a many-to-many set is prohibited

I have a Recipe and Ingredient class where i have a m2m placed on the ingredient model. I tested out the model in the admin panel and was working fine. However when i tried creating them in the shell i got an error(see the error below).

class Ingredient(models.Model):
    name = models.CharField(max_length=50)
    amount = models.IntegerField(default=1)
    ingredients = models.ManyToManyField(Recipe, related_name='ingredients')


class IngredientSerializer(ModelSerializer):
    class Meta:
        fields = ['name', 'amount']
        model = Ingredient



class Recipe(models.Model):
    owner = models.ForeignKey('auth.User', related_name='recipes', on_delete=models.CASCADE)
    name = models.CharField(max_length=100)
    description = models.TextField(max_length=200, blank=True)
    image = models.CharField(max_length=100, blank=True)


class RecipeSerializer(ModelSerializer):
        ingredients = IngredientSerializer(many=True)
        owner = ReadOnlyField(source='owner.username')

    class Meta:
        fields = ['owner', 'name', 'description', 'image', 'ingredients']
        model = Recipe

Shell Command

beefsoup = Recipe.objects.create(owner=user, name="beef", description="goot", image="httplo")
tomatoes = Ingredient.objects.create(ingredients=beefsoup ,name='tomatoes', amount=2)

Error
TypeError: Direct assignment to the forward side of a many-to-many set is prohibited. Use ingredients.set() instead.

Upvotes: 4

Views: 4522

Answers (1)

Victor Miroshnikov
Victor Miroshnikov

Reputation: 594

As the error message and Django Docs suggest, your snippet should look this way:

  beefsoup = Recipe.objects.create(owner=user, name="beef", description="goot", image="httplo")
  beefsoup.ingredients.create(name='tomatoes', amount=2)

Besides that, judging by model & property names, it seems that your relationship design is incorrect. It should rather look this way: 

class Ingredient(models.Model):
    name = models.CharField(max_length=50)
    amount = models.IntegerField(default=1)


class IngredientSerializer(ModelSerializer):
    class Meta:
        fields = ['name', 'amount']
        model = Ingredient


class Recipe(models.Model):
    owner = models.ForeignKey('auth.User', related_name='recipes', on_delete=models.CASCADE)
    name = models.CharField(max_length=100)
    description = models.TextField(max_length=200, blank=True)
    image = models.CharField(max_length=100, blank=True)
    ingredients = models.ManyToManyField(Ingredients, related_name='recipes')


class RecipeSerializer(ModelSerializer):
    ingredients = IngredientSerializer(many=True)
    owner = ReadOnlyField(source='owner.username')

    class Meta:
        fields = ['owner', 'name', 'description', 'image', 'ingredients']
        model = Recipe

Note that ingredients now reside in Recipe model.

Upvotes: 4

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