Extended Attribute¶

Resource models have the ability to be extended with extended attributes. Extended attributes helps in the situation where you are building a generic feature, but you wish to allow downstream application to add additional data fields into the generic resource model without having to redefine the storage implementation with additional fields.

For example, a generic Event model would probably have title, start_datetime and end_datetime on its model, and you have created multiple views to display the Event, such as ical_view and xml_view. Now, you are doing a project for CustomerA, which you need to add additional data fields to Event model, eg: department_name. Normally you would have to modify EventSchema and its respective db schema with additional fields, but with extended attributes, you can simply register a extended attribute provider for Event model which would store the value of department_name.

class morpfw.interfaces.IXattrProvider¶

abstract as_dict()¶: Returns dictionary representation of the data, where python objects such as datetime remains as python objects

abstract as_json()¶: Returns JSON-safe dictionary representation of the data. Any python objects are serialized into JSON-safe data type

abstract jsonschema() → dict¶: Returns JSON Schema for Xattr

abstract process_update(newdata: dict)¶: Validate received data and then update the extended attributes

abstract update(newdata: dict)¶: Update extended attributes

abstract property schema: Type[Any]¶: Schema to use for data validation

Registering Extended Attribute Provider¶

MorpFW provides a default implementation for extended attribute provider called FieldXattrProvider which stores extended attributes in xattr field of the resource.

To register an extended attribute provider for your model using FieldXattrProvider, add the following code:

import typing
from dataclasses import dataclass
from morpfw.crud.xattrprovider.fieldxattrprovider import FieldXattrProvider
import morpfw
from .app import App
from .model import PageModel


@dataclass
class PageXattrSchema(morpfw.BaseSchema):

    field1: typing.Optional[str] = None
    field2: typing.Optional[str] = None


class PageXattrProvider(FieldXattrProvider):

    schema = PageXattrSchema
    additional_properties = False


@App.xattrprovider(model=PageModel)
def get_xattrprovider(context):
    return PageXattrProvider(context)