How to include extra data in the Django serializer response?

Question

Hi, I am trying to make a livesearch with Django and jQuery. What I've done is make the javascript ask for some data with the getJSON function, then I've set up a view in Django that returns a JSON response automated by the Django serializer.

And this works well, it returns a json response with the text/javascript content-type. To avoid sending all the data, (alot that i dont need) i did this:

response.write(serializers.serialize("json", soknad_list, fields=('name', 'image', 'genre')))

But for instance, the 'genre' field is a manyToMany field, so is it possible to get the values from genre.all.0 for instance and not just the genre ID?

And the model has a function get_absolute _url, is it possible to include this in the JSON response, if so how?

So i guess my question is, is it possible to include stuff other than the raw field data in the JSON response, if not, how would you go about solving my problem?

Answer 1

Django's JSON serialization is based on simplejson, which you can use directly and extend at will to handle whatever kind of objects. So you mostly have two options here: either manually build a list of dicts with relevant data and pass it to simplejson.dumps() (which by default support strings, lists, dicts and numerics), or write your own json encoder that knows how to serialize your specific dataset. FWIW, here's a (not well tested but worked so far) Django model aware json encoder:

from django.utils import simplejson
from django.utils import datetime_safe
from django.utils.functional import Promise
from django.utils.translation import force_unicode
from django.utils.encoding import smart_unicode
from django.core.serializers.json import DjangoJSONEncoder

class ModelJSONEncoder(DjangoJSONEncoder):
    """
    (simplejson) DjangoJSONEncoder subclass that knows how to encode fields.

    (adated from django.serializers, which, strangely, didn't
     factor out this part of the algorithm)
    """
    def handle_field(self, obj, field):
        return smart_unicode(getattr(obj, field.name), strings_only=True)

    def handle_fk_field(self, obj, field):
        related = getattr(obj, field.name)
        if related is not None:
            if field.rel.field_name == related._meta.pk.name:
                # Related to remote object via primary key
                related = related._get_pk_val()
            else:
                # Related to remote object via other field
                related = getattr(related, field.rel.field_name)
        return smart_unicode(related, strings_only=True)

    def handle_m2m_field(self, obj, field):
        if field.creates_table:
            return [
                smart_unicode(related._get_pk_val(), strings_only=True)
                for related
                in getattr(obj, field.name).iterator()
                ]

    def handle_model(self, obj):
        dic = {}
        for field in obj._meta.local_fields:
            if field.serialize:
                if field.rel is None:
                    dic[field.name] = self.handle_field(obj, field)
                else:
                    dic[field.name] = self.handle_fk_field(obj, field)
        for field in obj._meta.many_to_many:
            if field.serialize:
                dic[field.name] = self.handle_m2m_field(obj, field)
        return dic

    def default(self, obj):
        if isinstance(o, Promise):
            return force_unicode(o)

        if isinstance(obj, Model):
            return self.handle_model(obj)

        return super(ModelJSONEncoder, self).default(obj)

HTH

Answer 2

I found out that the simplest thing was to not use the serializer at all. I dont know why I didnt think of this before, but i just used a generic object list view and changed the mimetype to text/javascript and made a JSON template insted of a html template.

Very simple, and that way i managed to get all the data i wanted into the JSON response. This way you can add everything that you can add to a html template into a JSON response, even paginating.

Example extraction of the view i created:

return object_list(request, queryset=object_list, template_name='search/results.js', template_object_name='result', paginate_by=12, mimetype='text/javascript')

Answer 3

I like the generic view solution, but, would you give to us more details.... thanks...

Answer 4

There is a handy django third party app / serializer that will allow you to include extra data. It also allows you to include model relations and exclude a list of fields.

It's available at http://code.google.com/p/wadofstuff/wiki/DjangoFullSerializers

Answer 5

thanks @sebalt, that worked.

@espen can you provide more details on the solution (urls & view & template)