ModelSerializer and custom properties on Model

[Josh Mahoney]

Hi,

How can I support custom Model properties with ModelSerializer?

Say I have:

class Foo(models.Model):

... normal Django Model fields ...

@property

def Bar(self):

return "some stuff" 

How could I have 'Bar' in my list of fields for the ModelSerializer and have that work? (this is currently throwing a KeyError in serializers.py in get_fields) 

[Tom Christie]

Hi Josh,

  You're looking for SerializerMethodField.  Documented here.

Cheers,

  Tom

[Tom Christie]

Apologies, I should have read the post more carefully.

You should be able to add model properties by adding a field to the serializer.

In this case...

    Bar = serializers.Field()

Although I'd probably recommend using a more conventional lowercase style for your property name.

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[Josh Mahoney]

Hi Tom,

Thanks for pointing me in the right direction... I missed this part of the documentation for some inexplicable reason. Anyway, I seem to have run into a bug here, although it is easily avoided. If the source attribute of Field is the same as the actual field name I get a KeyError. Filed here: https://github.com/tomchristie/django-rest-framework/issues/811

Best,
Josh

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[Josh Mahoney]

Apologies - that issue I filed was incorrect. However, I am still experiencing a KeyError on 'extracted_data' in line 206 of rest_framework/serializers.py in get_fields. The following is what I have and I can't see why it isn't working:

# serializers.py

class MasterSerializer(serializers.ModelSerializer):

    class Meta:

        model = Master

        extracted_data = serializers.Field(source='get_tabs_meta')

        statistics = serializers.Field()

        fields = ('id', 'sha256', 'file_size', 'file_type', 'file_subtype', 'extracted_data', 'valid', 'validated', 'statistics')

# models.py

class Master(models.Model):

    id = models.BigIntegerField(primary_key=True)

    sha256 = BlobField(unique=True)

    file_size = models.BigIntegerField()

    file_type = models.CharField(max_length=512)

    file_subtype = models.CharField(max_length=512)

    meta = BlobField()

    stats = BlobField()

    valid = models.BooleanField()

    validated = models.BooleanField()

    _tc_meta = None

    _stat_meta = None

    class Meta:

        db_table = u'master'

    def tc_meta(self):

        if self._tc_meta is None:

            tc_meta = meta_pb2.metadata_t()

            tc_meta.ParseFromString(base64.b16decode(self.meta))

            self._tc_meta = protobuf_json.pb2json(tc_meta)

        return self._tc_meta

    tc_meta.allow_tags = True

    def statistics(self):

        if self._stat_meta is None:

            stat_meta = stat_pb2.statistics_t()

            stat_meta.ParseFromString(base64.b16decode(self.stats))

            self._stat_meta = protobuf_json.pb2json(stat_meta)

        return self._stat_meta

    def get_tabs_meta(self):

        tm = self.tc_meta()

        return tm

# views.py

class MasterDetail(generics.RetrieveAPIView):

    queryset = Master.objects.all()

    lookup_field = 'sha256'

    serializer_class = MasterSerializer

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[Josh Mahoney]

Bah!! I'm an idiot. I had the fields under the "Meta" class, instead of at the MasterSerializer class level. Sometimes staring at something makes you blind. :) Problem fixed... carry on... nothing to see here...