How to use the pulpcore.app.models.Artifact.objects.all function in pulpcore

if data['file'].size != int(data['size']):
                raise serializers.ValidationError(_("The size did not match actual size of file."))
        else:
            data['size'] = data['file'].size

        for algorithm in hashlib.algorithms_guaranteed:
            if algorithm in models.Artifact.DIGEST_FIELDS:
                digest = data['file'].hashers[algorithm].hexdigest()

                if algorithm in data and digest != data[algorithm]:
                    raise serializers.ValidationError(_("The %s checksum did not match.")
                                                      % algorithm)
                else:
                    data[algorithm] = digest
                if algorithm in UNIQUE_ALGORITHMS:
                    validator = UniqueValidator(models.Artifact.objects.all(),
                                                message=_("{0} checksum must be "
                                                          "unique.").format(algorithm))
                    validator.field_name = algorithm
                    validator.instance = None
                    validator(digest)
        return data

- define its own `Meta` class should:
       - specify plugin content model
       - extend `fields` with plugin-specific ones
    """
    class Meta:
        model = Artifact
        fields = ['md5', 'sha1', 'sha224', 'sha256', 'sha384', 'sha512']


class ArtifactViewSet(NamedModelViewSet,
                      mixins.CreateModelMixin,
                      mixins.RetrieveModelMixin,
                      mixins.ListModelMixin,
                      mixins.DestroyModelMixin):
    endpoint_name = 'artifacts'
    queryset = Artifact.objects.all()
    serializer_class = ArtifactSerializer
    filterset_class = ArtifactFilter
    parser_classes = (MultiPartParser, FormParser)
    swagger_schema = ArtifactSchema

    def destroy(self, request, pk):
        """
        Remove Artifact only if it is not associated with any Content.
        """
        try:
            return super().destroy(request, pk)
        except models.ProtectedError:
            msg = _('The Artifact cannot be deleted because it is associated with Content.')
            data = {'detail': msg}
            return Response(data, status=status.HTTP_409_CONFLICT)

class DownloadCatalogSerializer(ModelSerializer):

    _href = serializers.HyperlinkedIdentityField(
        view_name='downloadcatalogs-detail',
    )

    url = serializers.CharField(
        help_text=_("The URL used to download the related artifact."),
        allow_blank=True, read_only=True,
    )

    artifact = serializers.HyperlinkedRelatedField(
        help_text=_("The artifact that is expected to be present at url"),
        queryset=models.Artifact.objects.all(),
        view_name="artifacts-detail"
    )

    importer = DetailNestedHyperlinkedRelatedField(
        parent_lookup_kwargs={'repository_name': 'repository__name'},
        queryset=models.Importer.objects.all(),
        help_text=_("The importer that contains the configuration necessary to access url."),
        lookup_field='name'
    )

    class Meta:
        model = models.DownloadCatalog
        fields = ModelSerializer.Meta.fields + ("artifact", "importer", "url",)

class ContentRelatedField(DetailRelatedField):
    """
    Serializer Field for use when relating to Content Detail Models
    """
    queryset = models.Content.objects.all()


class SingleContentArtifactField(RelatedField):
    """
    A serializer field for the '_artifacts' ManyToManyField on the Content model (single-artifact).
    """
    lookup_field = 'pk'
    view_name = 'artifacts-detail'
    queryset = models.Artifact.objects.all()
    allow_null = True

    def get_attribute(self, instance):
        """
        Returns the field from the instance that should be serialized using this serializer field.

        This serializer looks up the list of artifacts and returns only one, if any exist. If more
        than one exist, it throws and exception because this serializer is being used in an
        improper context.

        Args:
            instance (:class:`pulpcore.app.models.Content`): An instance of Content being
                serialized.

        Returns:
            A single Artifact model related to the instance of Content.

class DownloadCatalogSerializer(ModelSerializer):

    _href = serializers.HyperlinkedIdentityField(
        view_name='downloadcatalogs-detail',
    )

    url = serializers.CharField(
        help_text=_("The URL used to download the related artifact."),
        allow_blank=True, read_only=True,
    )

    artifact = serializers.HyperlinkedRelatedField(
        help_text=_("The artifact that is expected to be present at url"),
        queryset=models.Artifact.objects.all(),
        view_name="artifacts-detail"
    )

    importer = DetailNestedHyperlinkedRelatedField(
        parent_lookup_kwargs={'repository_name': 'repository__name'},
        queryset=models.Importer.objects.all(),
        help_text=_("The importer that contains the configuration necessary to access url."),
        lookup_field='name'
    )

    class Meta:
        model = models.DownloadCatalog
        fields = ModelSerializer.Meta.fields + ("artifact", "importer", "url",)

"sha224",
            "sha256",
            "sha384",
            "sha512",
        }


class ArtifactViewSet(
    NamedModelViewSet,
    mixins.CreateModelMixin,
    mixins.RetrieveModelMixin,
    mixins.ListModelMixin,
    mixins.DestroyModelMixin,
):
    endpoint_name = "artifacts"
    queryset = Artifact.objects.all()
    serializer_class = ArtifactSerializer
    filterset_class = ArtifactFilter

    def destroy(self, request, pk):
        """
        Remove Artifact only if it is not associated with any Content.
        """
        try:
            return super().destroy(request, pk)
        except models.ProtectedError:
            msg = _("The Artifact cannot be deleted because it is associated with Content.")
            data = {"detail": msg}
            return Response(data, status=status.HTTP_409_CONFLICT)


class ContentFilter(BaseFilterSet):

else:
            data["size"] = data["file"].size

        for algorithm in hashlib.algorithms_guaranteed:
            if algorithm in models.Artifact.DIGEST_FIELDS:
                digest = data["file"].hashers[algorithm].hexdigest()

                if algorithm in data and digest != data[algorithm]:
                    raise serializers.ValidationError(
                        _("The %s checksum did not match.") % algorithm
                    )
                else:
                    data[algorithm] = digest
                if algorithm in UNIQUE_ALGORITHMS:
                    validator = UniqueValidator(
                        models.Artifact.objects.all(),
                        message=_("{0} checksum must be " "unique.").format(algorithm),
                    )
                    validator.field_name = algorithm
                    validator.instance = None
                    validator(digest)
        return data