DB response

Our database layer functions did a couple of things right but what is missing is a structured return statement, almost like a contract. When the function executes successfully the API layer and our end-user received the value True. Not the most user-friendly response for sure.

Improving DB layer returns

A good place to start is by defining how the response will look like. It needs to convey several messages back to the API layer/user:

  • general success/failure when performing actions
  • an error message if an error happens
  • a resource_id, if there was a write to the database (like a donor sign-up)
  • a data structure to contain items read from a database (a list of donors for example)

I’ve been a fan of Python dataclasses since they were introduced back in Python 3.6 and the above-mentioned data structure is perfect for a dataclass.

Code changes

The DBResponse dataclass will be shared between all database mixins so a good place to create it is in chalicelib/__init__.py

from dataclasses import dataclass


@dataclass
class DBResponse:
    resource_id: str
    success: bool
    error_message: str
    return_value: dict

Using it in chalicelib/db_donor.py would go like this:

from uuid import uuid4
from . import DBResponse


class DonorMixin:

    def donor_signup(self, donor_dict):
        uid = str(uuid4()).split("-")[-1]
        db_response = DBResponse(resource_id="", success=False, error_message="", return_value={})

        try:
            self._table.put_item(
                Item={
                    "first_name": donor_dict.get("first_name"),
                    "city": donor_dict.get("city"),
                    "type": donor_dict.get("type"),
                    "email": donor_dict.get("email"),
                    "PK": f"DONOR#{uid}",
                }
            )
            self._logger.debug(f"Inserted donor '{donor_dict.get('email')}' into DynamoDB table '{self._table}'")

            db_response.success = True
            db_response.resource_id = uid

            return db_response

        except Exception as exc:
            db_response.success = False
            db_response.error_message = str(exc)

            self._logger.exception(exc)

        finally:
            return db_response

DIY

Please proceed to implement the DBResponse dataclass for the DonationMixin.

Solution