Feature request: alias generator for Query, Path or Header

Question

Feature request: alias generator for Query, Path or Header

Closed this issue a month ago · 23 comments

tonnico commented 3 months ago

Use case

In a BaseModel you can setup an alias_generator.

It would be release nice to have something configurable for e.g. Query

Solution/User Experience

Think about this:

@app.get("/")
def list_something(max_results: Annotated[int, Query(alias="maxResults")]) -> Response[str]:
    ...

could become something like this:

class CamelCaseQuery(Query):
    field_config = {"alias_generator": alias_generators.to_camel}

@app.get("/")
def list_something(max_results: Annotated[int, CamelCaseQuery()]) -> Response[str]:
    ...

Alternative solutions

Acknowledgment

This feature request meets Powertools for AWS Lambda (Python) Tenets
Should this be considered in other Powertools for AWS Lambda languages? i.e. Java, TypeScript, and .NET

Answer 1 · 2025-07-25T12:16:07.000Z

Hi @tonnico, thanks for opening this issue! I know about the alias generator in Pydantic, but I might not understand your point here. Can you explain a bit more?

Thanks

Answer 2 · 2025-07-25T14:21:03.000Z

Our default for query parameters is camelCase. It would be nice to setup this without repeating any time with an alias.
Maybe this should be a feature for pydantic FieldInfo?

Answer 3 · 2025-07-25T17:38:55.000Z

Our default for query parameters is camelCase. It would be nice to setup this without repeating any time with an alias. Maybe this should be a feature for pydantic FieldInfo?

Aaa, thanks for explaining the use case, I get it now. The problem here is that Query inherits from FieldInfo and not from BaseModel, so there's no model_config that allows auto-transformation to camelCase. Also, the Pydantic documentation says (search for "camel") that the correct way is to use alias (which is what you're doing). So, yes, I think we can open a feature request in Pydantic.

I tried searching and didn't find anything: https://github.com/pydantic/pydantic/issues?q=sort%3Aupdated-desc%20is%3Aissue%20state%3Aopen%20fieldInfo%20camel

What do you think?

Answer 4 · 2025-07-27T06:59:10.000Z

I think it is not possible to add such information to the type on some way. Probably the best solution would be to add something similar to FastAPI. There you are able to use complete BaseModel's for queries, headers and body.

class Q(BaseModel):
    model_config = {"alias_generator": to_camel}

    my_value: str

@app.get("/")
def list(q: Annotated[Q, Query()]):
    return q.my_value

Answer 5 · 2025-07-28T09:47:43.000Z

Yeah, that make sense for me, but in this case we need to support Pydantic models when using Query/Headers and we don't support that yet. Do you want to submit a PR to implement it? I'd love to have this support and tbh I'm think to implement this soon.

Answer 6 · 2025-07-28T13:35:22.000Z

I would love to implement this. However, I don't think I could start any earlier than November.

Answer 7 · 2025-07-29T17:18:17.000Z

I would love to implement this. However, I don't think I could start any earlier than November.

Hey, thats ok @tonnico! I'll try to work on this in the next week and ping you for a review.

Answer 8 · 2025-07-29T17:22:17.000Z

Sounds good, looking forward to it!

Answer 9 · 2025-07-30T22:16:26.000Z

I'm working on this PR to add this support: #7076

Answer 10 · 2025-08-04T15:45:57.000Z

Thanks, I'm looking into it.

I'm testing with this minimal.

from typing import Annotated
from aws_lambda_powertools.event_handler import APIGatewayRestResolver
from pydantic import BaseModel, StringConstraints
from aws_lambda_powertools.event_handler.openapi.params import Query

app = APIGatewayRestResolver(enable_validation=True)


class QueryParams(BaseModel):
    full_name: Annotated[str, StringConstraints(min_length=5)]


@app.get("/query-model")
def query_model(
    params: Annotated[QueryParams, Query()],
):
    return {"fullName": params.full_name}

While a missing value looks good.

{"statusCode":422,"detail":[{"loc":["query","full_name"],"type":"missing"}]}

A request with full_name=abc gives me this error

{"statusCode":422,"detail":[{"loc":["query","params"],"type":"value_error"}]}

Answer 11 · 2025-08-04T16:06:04.000Z

Hi @tonnico, thanks a lot for validating this... but this is the expected behavior, isn't it? You're using Pydantic's StringConstraints and saying the minimum length is 5, but you're passing a string of length 3 and getting a validation error.

Running this same code with a valid string:

Am I missing something?

Answer 12 · 2025-08-04T16:08:00.000Z

Hmmm, maybe you expected a better error description, because this should be a constraint validation error due to the minimum string length, is that it?

Answer 13 · 2025-08-04T16:31:02.000Z

Yes, at least I would expect something like {"loc":["query","full_name"]... and not {"loc":["query","params"]...

Answer 14 · 2025-08-04T16:35:56.000Z

Yes, at least I would expect something like {"loc":["query","full_name"]... and not {"loc":["query","params"]...

Ok, thanks for confirming. I need to work here: https://github.com/aws-powertools/powertools-lambda-python/pull/7076/files#diff-f2877be00a4e8e930e5ca73ba8d56caf0eba726919a6b7c5349681bda5ca442cR356

Let me see if I can improve the error extraction message in this case. Any insight/debugging are welcome.

Answer 15 · 2025-08-04T19:23:14.000Z

Hey @tonnico I made some changes in the PR to improve the error message + header serialization/validation, which was failing with fields using _.

Can you pls try again and let me know what you think? Also, if you have any advanced use case I'd love to test it.

Commit: 7c49d72

Btw, I still need to clean this code and improve some areas that I'm not happy, but I just want to see if this is good enough to ship to production after this optimization.

Answer 16 · 2025-08-04T21:28:58.000Z

Hey,

I made a little repo for simple testing with some more advanced models.

https://github.com/tonnico/powertools-minimal

Just clone this repo close to the powertools and try it out.

.
├── powertools-lambda-python
└── powertools-minimal

currently the alias is not working as expected.

Answer 17 · 2025-08-04T21:57:08.000Z

Thanks for sharing @tonnico, this is really helpful! I know what is going, I need to make the validation method more generic. I'll work on that this week.

Answer 18 · 2025-08-08T13:41:43.000Z

Hi @tonnico, I made some additional changes to the PR and I'm validating your example! Everything seems to be working, but I'm still testing other things.

I hope to solve all the issues by next week, and then I'll clean up the code and tests.

Answer 19 · 2025-08-10T11:21:41.000Z

Very nice work. I'm looking forward to test this in my productive code. Currently I'm in vacation for 2 weeks.

One point I was missing in the test section is a multi value query. E.g. endpoint?attr=a&attr=b would become "attr": ["a", "b"]. While this work in current annotations without BaseModel support I will expect that this will still work. So I think a test would be very nice.

Answer 20 · 2025-08-10T16:46:35.000Z

@leandrodamascena I've added an example in my repo. Hope this helps.

Answer 21 · 2025-08-25T15:10:32.000Z

@leandrodamascena Is it ok for you, when I create a PR on top of yours? I have solved some errors on my computer.

Answer 22 · 2025-08-25T15:51:45.000Z

@leandrodamascena Is it ok for you, when I create a PR on top of yours? I have solved some errors on my computer.

Heyy @tonnico sure thing! Create another one and then we can close mine!

Answer 23 · 2025-10-10T13:08:37.000Z

Warning

This issue is now closed. Please be mindful that future comments are hard for our team to see.
If you need more assistance, please either reopen the issue, or open a new issue referencing this one.
If you wish to keep having a conversation with other community members under this issue feel free to do so.