How to save the parse json array values to the database in django python rest api,by using models.py , serializers.py and views.py

Question

I want save the category and their subcategories to the database and here each category have a multiple subcategories.Could you please help me to save the user,category and multiple subcategories corresponding to category.Models.py, Serializers.py, Views.py and incomming request is attached.

Models.py

class SavingCategoryandPreferences(models.Model):

   user = models.ForeignKey(User, related_name='user')
   news_category = models.ForeignKey(NewsCategory)
   subcategories= models.ManyToManyField(NewsSubCategory, related_name='sub')
   sort_order = models.IntegerField(default=0)
   slug = AutoSlugField(populate_from='subcategories_id', separator='', editable=True)
   created_time = models.DateTimeField("Created Date", auto_now_add=True)

Serializers.py

class MobilecatsubSerializer(serializers.ModelSerializer):
  class Meta:
    model = SavingCategoryandPreferences
    fields = ('id', 'user', 'subcategories', 'news_category',)

Views.py

class MobileCatsubViewswt(viewsets.ModelViewSet):
  serializer_class = serializers.MobilecatsubSerializer
  queryset = SavingCategoryandPreferences.objects.all()

Incomming Request

{
 "user":"39",
 "news_category":"22",
 "subcategories": [
    {"sub_id":"1"},
    {"sub_id":"2"}
  ]
}

Answer 1

By default DRF serializers.ModelSerializer defines all related fields as PrimaryKeyRelatedField . For to-many relationships ( many=True ) ie reverse FK or many-to-many, it implicitly creates an instance of ManyRelatedField with the original field ( PrimaryKeyRelatedField in this case) kept as the child_relation instance attribute, which in turn is used in the to_internal_value method of ManyRelatedField to actually do validation for each incoming item (primary keys in this case) passed in as list elements for the field.

The above is a long way of saying that you can only pass the primary keys of the related NewsSubCategory instances in a list eg:

{
 "user":"39",
 "news_category":"22",
 "subcategories": [1, 2]
}

You can even pass the primary keys as strings.

---

Now, if you don't have any control over how and in what format the data is passed, you can override to_internal_value method of MobilecatsubSerializer to extract the primary keys from the input data and update the input data dict with them eg:

class MobilecatsubSerializer(serializers.ModelSerializer):

    class Meta:
        model = SavingCategoryandPreferences
        fields = ('id', 'user', 'subcategories', 'news_category',)

    def to_internal_value(self, data):
        if 'subcategories' in data:
            # Change this if needed
            spams = [dct['sub_id'] for dct in data['subcategories']]
            data.update(subcategories=subcategories)
        return super().to_internal_value(data)

---

If you feel overly ambitious you can go ahead and instead override the to_internal_value method of the PrimaryKeyRelatedField (or anything you use for the field) to do the serialization of the values there, but it would be a bad idea as all other serializers that have PrimaryKeyRelatedField also needs to go through this needlessly. But if for some reason, you want to follow this path, it would better to subclass PrimaryKeyRelatedField , do serialization overriding to_internal_value like the way I did above, and set this one explicitly as the serializer for the subcategories field.