Issue number: #5476

Summary

Changes

The current implementation of event_parser fails when a TypeAdapter instance is provided as the model. This is due to an attempt to cast an existing TypeAdapter into a new TypeAdapter, which results in a PydanticSchemaGenerationError.

Changes Made

1. Modified _retrieve_or_set_model_from_cache function to check if the input is already a TypeAdapter instance.
2. If the input is a TypeAdapter, it's returned directly from the cache without additional wrapping.
3. Maintained backwards compatibility for non-TypeAdapter models.

User experience

This code works now.

from typing import Literal, Union, Annotated

from pydantic import Field, TypeAdapter

# from aws_lambda_powertools.utilities.parser import event_parser

from aws_lambda_powertools.utilities.parser.models.event_bridge import EventBridgeModel
from aws_lambda_powertools.utilities.parser.models.s3 import (
    S3EventNotificationEventBridgeDetailModel,
)

class S3EventNotificationEventBridgeModel(EventBridgeModel):
    detail: S3EventNotificationEventBridgeDetailModel
    source: Literal["aws.s3"]


class ScheduledNotificationEventBridgeModel(EventBridgeModel):
    source: Literal["aws.events"]


EventBridgeSource = Annotated[
    Union[S3EventNotificationEventBridgeModel, ScheduledNotificationEventBridgeModel],
    Field(discriminator="source"),
]

EventBridgeModelAdapter = TypeAdapter(Union[EventBridgeSource, EventBridgeModel])

@event_parser(model=EventBridgeModelAdapter)
def handler(event: EventBridgeModelAdapter, context):
    print(f'Got event, parsed into {type(event)=}')

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

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