Copying only non-relation attributes django/python

Question

I am copying a model object to another, but I want that it doesn’t copy the relations

For example, assume you have a model like this:

class Dish(models.Model):
    name = models.CharField(max_length=100)
    description = models.CharField(max_length=500)
    category = models.ForeignKey(Category, on_delete=models.CASCADE, default=1)

    def __str__(self):
        return self.name

Then I do:

            my_dish = Dish.objects.get(pk=dish.id)
            serializer = Dish_Serializer(my_dish)
            my_new_object = serializer.data

I want my_new_object to include only those attributes that are not relations, in this case, name and description.

How do I do that without accessing name and description directly?

Asked By: Rafael

||

Source

Answer 1

I assume in your serializer you don’t want to explicitly define which field to serialize. Otherwise you could do the following:

class Dish_Serializer(serializers.ModelSerializer):
    class Meta:
        model = Dish
        fields = ['id','name', 'description']

You probably can define these fields dynamically:

        fields = [f.name for f in Dish._meta.concrete_fields]

or

        fields = [f.name for f in Dish._meta.fields if not isinstance(f,ForeignKey)]

Answered By: André Guerra

Answer 2

Ultimately, you want my_new_object in dictionary format and as per condition pk will give you only one object of dish.
So, you can do this instead :

my_new_object = Dish.objects.filter(pk=dish.id).values("name", "description")[0]

It will give you exact what you want, just declare the fields you need in values as an attribute fields.

Answered By: techbipin

Answer 3

You can remove a field from your serializer using .fields.pop(field_name) method like the below example According that I took from Dynamically modifying fields ^[drf-docs]:

class DynamicFieldsModelSerializer(serializers.ModelSerializer):
   """
   A ModelSerializer that takes an additional `fields` argument that
   controls which fields should be displayed.
   """

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

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

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

Also, you can do this in your view like the below code snippet:

my_dish = Dish.objects.get(pk=dish.id)
serializer = Dish_Serializer(my_dish)
desired_fields = {'id', 'name', 'description'}
all_fields = set(serializer.fields)
for field in all_fields:
    if field not in desired_fields:
        serializer.fields.pop(field)
my_new_object = serializer.data

Answered By: Javad

Copying only non-relation attributes django/python

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