[Django]-Serializing Foreign Key objects in Django

UPDATE:
Actually Manoj’s solution is a bit outdated, Wad of Stuff’s serializer has been left un-updated for some time and when I tried that, it seems that it does not support Django 1.6 anymore.

However, take a look at Django’s official doc here. It does provide some way around using the built-in natural key. It seems that django’s built-in serializer has a a little problem supporting using ImageField as part of the natural key. But that can be easily fixed by your self.

I’m aware this topic is years old, however, I’m sharing my solution for the people still searching for an answer (during my search, I ended up here).

Please note, I was looking for a simple function which would give me nested (foreign key) objects/dictionaries (which could contain nested (foreign key) objects/dictionaries as well) within my model/queryset which I could then convert to JSON.

In my models.py, I have a custom function (not within a model class):

Models.py

def django_sub_dict(obj):
    allowed_fields = obj.allowed_fields() # pick the list containing the requested fields
    sub_dict = {}
    for field in obj._meta.fields: # go through all the fields of the model (obj)
        if field.name in allowed_fields: # be sure to only pick fields requested
            if field.is_relation: # will result in true if it's a foreign key
                sub_dict[field.name] = django_sub_dict(
                    getattr(obj, field.name)) # call this function, with a new object, the model which is being referred to by the foreign key.
            else: # not a foreign key? Just include the value (e.g., float, integer, string)
                sub_dict[field.name] = getattr(obj, field.name)
    return sub_dict # returns the dict generated

This function loops through all the fields in a models.Model object, if the models.Model is provided. I call the function within a model as follows (for completeness sake, including one entire model):

the same Models.py

class sheet_categories(models.Model):
    id = models.AutoField(primary_key=True, unique=True)
    create_date = models.DateField(auto_now_add=True)
    last_change = models.DateField(auto_now=True)
    name = models.CharField(max_length=128)
    sheet_type = models.ForeignKey(
        sheet_types, models.SET_NULL, blank=False, null=True)
    balance_sheet_sort = models.IntegerField(unique=True)

    def allowed_fields(self):
        return [
                'name',
                'sheet_type',
                'balance_sheet_sort',
                ]

    def natural_key(self):
        return django_sub_dict(self) # call the custom function (which is included in this models.py)

Note:
The nested JSON objects will only contain fields which are included in the allowed_fields of a model. Thus not including sensitive information.

To ultimately generate a JSON, I have the following view in my views.py.

views.py

class BalanceSheetData(ListView): # I believe this doesn't have to **be** a ListView.
    model = models.sheet_categories

    def get_queryset(self):
        return super().get_queryset().filter() # the filter is for future purposes. For now, not relevant

    def get(self, request, *args, **kwargs):
        context = {
            'queryset': serializers.serialize("json",
                                          self.get_queryset(),
                                          use_natural_foreign_keys=True, # this or the one below makes django include the natural_key() within a model. Not sure.
                                          use_natural_primary_keys=True, # this or the one above makes django include the natural_key() within a model. Not sure.
                                          ),
        }
        return JsonResponse(context)

This ultimately provided me with all the nested details I required in a JSON response. Although I do not share the JSON response, as this one is barely readable.

Feel free to comment.

You can find more information on this ticket:

Allow In-depth serialization by specifying depth to follow relationship
https://code.djangoproject.com/ticket/4656

Adding a newer answer to this older question: I created and recently published django-serializable-model as an easily extensible way to serialize models, managers, and querysets. When your models extend SerializableModel, they receive an overridable .serialize method that has built-in support for all relations.

Using your example, once all of the involved models extend SerializableModel:

joins = ['object_type', 'individual']
artifact = Artifact.objects.select_related(*joins).get(pk=pk)
artifact.serialize(*joins)

Calling .serialize with the relations as arguments will have the library recurse over the related objects, calling .serialize on them as well. This returns a dictionary that looks like:

{
  'id': 1,
  'year_of_origin': 2010,
  'name': 'Dummy Title',
  'notes': '',
  'object_type_id': 1,
  'individual_id': 1,
  'object_type': { ... nested object here ... },
  'individual': { ... nested object here ... }
}

You can then call json.dumps on this dictionary to transform it to JSON.

By default, extending SerializableModel will also set the model’s manager to SerializableManager (you can extend it yourself if you’re using a custom manager) which uses SerializableQuerySet. This means you can call .serialize on a manager or queryset as well:

artifacts = Artifact.objects.select_related(*joins).all()
artifacts.serialize(*joins)

This simply calls .serialize on each model object in the queryset, returning a list of dictionaries in the same format as above.

django-serializable-model also allows you to easily override the default behavior on a per model basis, giving you the ability to do things like: add allowlists or denylists applied to each model’s .serialize, always serialize certain joins (so you don’t have to add them as arguments all the time), and more!