How to deal with nested serializer fields in Django Rest Framework?

Question

I have nested serializer (AmountSerializer). I need a field meal_name in one ViewSet. But when this field is nested, I don't need it to be seen in endpoint(in MealSerializer). How to exclude field from nested serializer when is it actually nested? models.py:

class MealType(models.Model):
    name = models.TextField()

    def __str__(self):
        return self.name

class Ingredient(models.Model):
    name = models.TextField()
    
    def __str__(self):
        return self.name

class Meal(models.Model):
    name = models.TextField()
    type = models.ForeignKey(MealType, on_delete=models.CASCADE, default=None)
    recipe = models.TextField()
    photo = models.ImageField(null=True, height_field=None, width_field=None, max_length=None,upload_to='media/')
    ingredients = models.ManyToManyField(Ingredient)

    def __str__(self):
        return self.name    

class IngredientAmount(models.Model):
    ingredient_name = models.ForeignKey(Ingredient, on_delete=models.CASCADE, default=None)
    amount = models.FloatField(default=None)
    meal = models.ForeignKey(Meal, on_delete=models.CASCADE, default=None, related_name='meal_id')

    class Meta:
        ordering = ['meal']

    def __str__(self):
        return self.ingredient_name

serializers.py:

class AmountSerializer(serializers.ModelSerializer):
    ingredient_name= serializers.ReadOnlyField(source='ingredient_name.name')
    -->#meal_name = serializers.ReadOnlyField(source='meal.name')
       #I CAN'T use ReadOnlyField( #with write_only=True)
       #i trired use PrimaryKeyRelatedField
       # butgot  AssertionError: Relational field must provide a `queryset` argument, override `get_queryset`, or set read_only=`True`.
    class Meta:
        model = IngredientAmount    
        fields = ('ingredient_name','amount','meal_name')

class MealSerializer(serializers.ModelSerializer):
    type_name= serializers.ReadOnlyField(source='type.name')
    ingredients = serializers.SlugRelatedField(read_only=True, slug_field='name', many=True)   
    amount = AmountSerializer(read_only=True,  many=True,source='meal_id')
    
    class Meta:
        model = Meal
        fields = ('id', 'name', 'type_name', 'recipe', 'photo', 'ingredients','amount')

user_5186565 · Answer

I'd rather use a trick to exclude some of the fields that are not needed in certain situations. You can inherit your serializer from ExcludeFieldsModelSerializer, and exclude any fields that you want so that the serializer will not serialize that field.

class ExcludeFieldsModelSerializer(serializers.ModelSerializer):
    """
    A ModelSerializer that takes an additional `exclude_fields` argument that
    controls which fields should be excluded from the serializer.
    Plagiarised from https://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields
    """

    def __init__(self, *args, **kwargs):
        # Don't pass the 'exclude_fields' arg up to the superclass
        exclude_fields = kwargs.pop('exclude_fields', None)

        # Instantiate the superclass normally
        super(ExcludeFieldsModelSerializer, self).__init__(*args, **kwargs)

        if exclude_fields is not None:
            # Drop any fields that are specified in the `exclude_fields` argument.
            drop = set(exclude_fields)
            for field_name in drop:
                self.fields.pop(field_name)


class AmountSerializer(ExcludeFieldsModelSerializer):
    ingredient_name= serializers.ReadOnlyField(source='ingredient_name.name')
    meal_name = serializers.CharField(read_only=True, source='meal.name')


    class Meta:
        model = IngredientAmount    
        fields = ('ingredient_name','amount','meal_name')


class MealSerializer(serializers.ModelSerializer):
    type_name= serializers.ReadOnlyField(source='type.name')
    ingredients = serializers.SlugRelatedField(read_only=True, slug_field='name', many=True)   
    amount = AmountSerializer(read_only=True,  many=True, source='meal_id', exclude_fields={'meal_name'})
    
    class Meta:
        model = Meal
        fields = ('id', 'name', 'type_name', 'recipe', 'photo', 'ingredients','amount')

How to deal with nested serializer fields in Django Rest Framework?

1 Answers