Issue number: #4300

Summary

Changes

The current implementation of the Data Validation does not natively support serializing some types of objects, including SQLAlchemy model objects and other custom classes that may not have a default serialization mechanism. This can lead to issues when trying to return these objects as the error is confuse.

In this PR, we are adding more robust exception handling and a clear message for cases where the object to be serialized is not supported.

Example of this implementation:

from typing import Any
from json import JSONEncoder
from dataclasses import is_dataclass, asdict
from sqlalchemy.orm.base import InstrumentedAttribute
from pydantic.main import ModelMetaclass

class UnsupportedObjectEncoder(JSONEncoder):
    def default(self, obj: Any) -> Any:
        if isinstance(obj, InstrumentedAttribute):
            return str(obj)
        elif is_dataclass(obj):
            return asdict(obj)
        elif isinstance(obj, ModelMetaclass):
            return obj.dict()
        else:
            try:
                return super().default(obj)
            except TypeError:
                # Handle unsupported objects by returning a default representation
                return str(obj)

def custom_serializer(obj: Any) -> str:
    return json.dumps(obj, separators=(",", ":"), cls=UnsupportedObjectEncoder)

app = APIGatewayRestResolver(enable_validation=True, serializer=custom_serializer)

User experience

Before this implementation, the customer received an incomprehensible error like:

Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/aws_lambda_powertools/event_handler/openapi/encoders.py", line 272, in _dump_other
backend-1  |
    data = dict(obj)
           ^^^^^^^^^
TypeError: cannot convert dictionary update sequence element #0 to a sequence
backend-1  |
During handling of the above exception, another exception occurred:
backend-1  |
Traceback (most recent call last):
  File "/usr/local/lib/python3.11/site-packages/aws_lambda_powertools/event_handler/openapi/encoders.py", line 276, in _dump_other
    data = vars(obj)

Now we've added a clear message in the exception

[ERROR] EncoderError: ('Unable to serializer the object <app.MyClass object at 0x7ffff27f45c0> as it is not a supported type. Error details: [TypeError("\'MyClass\' object is not iterable"), TypeError(\'vars() argument must have __dict__ attribute\')]', 'See: https://docs.powertools.aws.dev/lambda/python/latest/core/event_handler/api_gateway/#serializing-objects')

Checklist

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• Meet tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Acknowledgment

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