django-rest-framework access field inside serializer

Question

So I have a model like this

class DataSheet(BaseModel):
    """
    Represents a single dataSheet.
    dataSheets have their own model at the core. Model data is added to
    the dataSheets in the form of separate records.
    """

    class Meta:
        verbose_name = 'datasheet'
        verbose_name_plural = 'datasheets'
        ordering = ['position', 'cluster']
        required_db_features = {
            'supports_deferrable_unique_constraints',
        }
        constraints = [
            models.UniqueConstraint(
                fields=['position', 'cluster'],
                name='deferrable_unique_datasheet_position',
                deferrable=models.Deferrable.DEFERRED
            )
        ]

    def __str__(self):
        return self.name

    objects = managers.DataSheetsManager()
    positions = managers.PositionalManager()
    position = models.PositiveSmallIntegerField(db_index=True, editable=True)
    name = models.CharField(max_length=100, validators=[MinLengthValidator(2)], db_index=True)
    description = models.CharField(max_length=1024, null=True, blank=True, db_index=True)
    owner = models.ForeignKey('api_backend.Member', on_delete=models.CASCADE, db_index=True, editable=False)
    fields = models.ManyToManyField('api_backend.Field')
    overwrites = models.ManyToManyField('api_backend.RoleOverwrite')
    parent = models.ForeignKey('api_backend.Category', on_delete=models.CASCADE, null=True, blank=True)
    cluster = models.ForeignKey('api_backend.Cluster', on_delete=models.CASCADE, editable=False)

    REQUIRED_FIELDS = [name, owner, cluster]

and a serializer like this

class DataSheetSerializer(serializers.ModelSerializer):
    """
    A serialized DataSheet Object.
    Datasheets have their own:
        - array of fields
        - array of role-overwrites
    """

    def get_fields(self):
        fields = super(DataSheetSerializer, self).get_fields()
        fields['parent'].queryset = self.cluster.categories.all()

        return fields

    class Meta:
        model = DataSheet
        read_only_fields = ['position']
        fields = '__all__'

    # need to make sure that the parent category of the datasheet
    # belongs to the datasheet's cluster only.

    fields = partial.PartialFieldSerializer(many=True, read_only=True)
    overwrites = partial.PartialOverWriteSerializer(many=True, read_only=True)

the thing is, I want to access the serializer model's cluster field inside of the get_fields method. However, I couldn't do the same. Can someone help me?

I've seen other answers involving initial_data, but that doesn't work here.

fields['parent'].queryset = self.cluster.categories.all()

cluster is an unresolved reference here.

Ashwin Bande · Accepted Answer · 2021-01-11 07:19:42Z

1

self in get_fields is DataSheetSerializer instance not DataSheet model instance. hence it should not have cluster property. you can not access model DataSheet instance in get_fields as it gets fields from class DataSheet not from its instance. you can validate the field like

class DataSheetSerializer(serializers.ModelSerializer):
    # ... other code

    def validate(self, data):
         parent = data.get('parent')
         # check if parent is valid i.e in queryset
         # if yes return data
         # else raise serializers.validationError

answered Jan 11, 2021 at 7:19

Ashwin Bande

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