Graph/pydantic

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pydantic

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Updated4/30/2026

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You can use the pattern argument directly on the Field object. — For email validation specifically, Pydantic provides a dedicated type called EmailStr. Tension: schema_extra is for API documentation, not for validation. Outcome: EmailStr ensures that any data assigned to the email field will be validated against a well-tested email regex.

REQUIRESSolution

Parse your dictionary from the query — When `baz` will receive the Json string, it will be parsed into a dictionary. Tension: This method changes the openapi schema, so swagger will render `baz` as a file input. Outcome: you can use your custom Json loader type that will render as a textarea.

REQUIRESSolution

You can use `@model_serializer` to achieve this: — This will work as a FastAPI response model. Tension: but will still generate an unnested JSON schema in the OpenAPI documentation. Outcome: return {k: v for k, v in model_iter(self)}.

REQUIRESSolution

write the name of the model as a string — One possible solution is to write the name of the model as a string. Tension: This way, linked models are stored where it enhances readability, or they can be moved to a separate file. Outcome: reorganize models if I encounter such errors.

REQUIRESSolution

Replace the dependency in one of the schema files with the name in quotations — from typing import List from pydantic import BaseModel. Tension: and don't import it there. Outcome: blogs: List["ShowBlog"].

REQUIRESSolution

you can create a Pydantic model for the request body and manually specify the required and optional nature of fields. Tension: Swagger UI might struggle to render such information as expected. Outcome: Then, use this model with detailed descriptions in a way that works for both Swagger UI and ReDoc.

REQUIRESSolution

author_id: int = None # Case 3: works — defining optional fields in Pydantic models. Tension: when I use `author_id: int | None`, I get an error saying that a required field is missing. Outcome: author_id: Optional[int] = None # the original way.

REQUIRESSolution

Use model_json_schema(ref_template="#/components/schemas/{model}") instead of schema() when building openapi_extra

REQUIRESSolution

Use this model for response validation — And you can do use Pydantic validation. Outcome: or use Depends() with Pydantic model.

REQUIRESSolution

or use Depends() with Pydantic model — from fastapi import APIRouter. Outcome: async def add_job(job: Job = Depends()):.

REQUIRESSolution

from openai.types.chat.completion_create_params import CompletionCreateParamsBase — def chat_completions(body: Annotated[dict, CompletionCreateParamsBase]):. Tension: its no arguments in swagger, but you can see errors in the response. Outcome: ta.validate_python(body).

REQUIRESSolution

You should use `Field` with the `default_factory` parameter for this. — If you don't pass these in your JSON, they will always use the same default value. Tension: they will always use the same default value, regardless of the time the notification was received. Outcome: Here's a fixed version, based on the model dump you provided:.

REQUIRESSolution

You can get the actual string which is in json format from `Query` — from `Query`, then `model_validate_json` it to get your `MyParam` object. Tension: it would be nice for `fastapi` to do this for me directly in the function declaration. Outcome: async def get_param( json_str: Annotated[str, Query(description="json-encoded dictionary")], ) -> MyParam: return MyParam.model_validate_json(json_str).

REQUIRESSolution

such a dependency could be to validate that the name attribute is a full name. Tension: the dependency in your example needs to return a Person object.

PERTAIN_TOProblem

when I try to insert an e-mail that does not match the pattern it still does get inserted into the database — I'm currently working on an api using fastapi and sqlmodel. Tension: I've read in some github issues that the regex parameter is not working properlly with pydantic. Outcome: You need instead to use a Pydantic-native validation method.

PERTAIN_TOProblem

Normally, the response looks like this: — I have a model, called Candidate that I'm trying to return, two of the fields refer to another model, StaffMember. Tension: However, I don't want any nested fields.

PERTAIN_TOProblem

String literals such as `toys:["ToyResponse"]`, this method still causes circular import errors. Tension: you are still importing the class to resolve the type. Outcome: doesnt work when a child import a parent.

PERTAIN_TOProblem

objects seem to be assumed to arrive in the body in `fastapi` — I'm trying to receive a nontrivial query parameter object. Tension: I've had to do something like this on the server. Outcome: it would be nice for `fastapi` to do this for me directly in the function declaration.

PERTAIN_TOProblem

The route responds with a 422 Unprocessable Entity status code. — if the function declares the input parameter with `Annotated` and `Depends`. Tension: I am unable to run the tests with `pytest`. Outcome: The Main issue remains unsolved.

That schema_extra is for API documentation, not for validation. — SQLModel is built on top of Pydantic. Tension: The pattern you've specified is only added to (basically) Swagger. Outcome: You can use the pattern argument directly on the Field object.

AFFECTSRootCause

"Input should be a valid dictionary", "input": "{\"abc\":\"def\"}". Tension: the encoding should be correct.

AFFECTSRootCause

created_by": { "fname": "System", "sname": "Default", "full_name": "System Default" } — two of the fields refer to another model, StaffMember. Tension: I don't want any nested fields. Outcome: This will work as a FastAPI response model, but will still generate an unnested JSON schema in the OpenAPI documentation.

AFFECTSRootCause

To resolve the above issue, I added the below redirect URL to the Web Platform in the Api App registration. — cross-origin authorization code redemption. Outcome: After adding the redirect URL, I ran the application.

AFFECTSRootCause

from src.schemas.blog import ShowBlog # Import causing circular dependency. Tension: ImportError: cannot import name 'ShowBlog' from partially initialized module 'src.schemas.blog'. Outcome: write the name of the model as a string.

AFFECTSRootCause

the `TYPE_CHECK` boolean must be checked at every place where the circular import types are being used. Tension: which results in an undefined error when accessing the type. Outcome: code inside if TYPE_CHECKING: is not executed at runtime.

AFFECTSRootCause

Swagger UI and ReDoc handle documentation differently — when using the built-in FastAPI types like Body, Query, or Header. Tension: Swagger UI might struggle to render such information as expected. Outcome: FastAPI’s behavior might be due to how Swagger UI interacts with FastAPI’s type annotations and the use of Annotated.

AFFECTSRootCause

there is no default value. The annotations don't actually do anything by themselves. — Pydantic for data validation in a Python project. Outcome: All of the options bellow work, and they are pretty much equivalent under the hood.

AFFECTSRootCause

Pydantic v2 uses model_json_schema(), while schema() no longer generates the needed schema for RootModel unions with discriminators

AFFECTSRootCause

The API schema is using the same SQLModel database model for serialization, so Pydantic follows the field type (`list[Category]`) and emits full `Category` objects instead of deriving strings.

AFFECTSRootCause

Pydantic/SQLModel does not automatically map nested object attributes (like item.name) into a differently typed field (like list[str]) during validation.

AFFECTSRootCause

I'm using the method POST only for inserting data and not updating it — when I'm calling the POST endpoint with partial data or with keys I don't specify in my class.

AFFECTSRootCause

CompletionCreateParams - inherited from TypedDict inherited from TypedDict. — pydantic/type_adapter.py. Tension: AttributeError: __pydantic_core_schema__.

AFFECTSRootCause

FastAPI's request-body parsing and Pydantic model validation are tied to the declared model type; excluding fields at the annotation/body level does not reliably integrate with Pydantic's normal model construction and validation flow. Using private/hidden fields is the intended Pydantic mechanism, but `Field()` cannot be used with private attributes in Pydantic v2.

AFFECTSRootCause

`EmailNotificationSystem` extends `EmailNotification`, but also has it as a member. Tension: Pydantic fails saying all the fields inside the email_notification that I'm setting with `email=email_notification` are missing. Outcome: This probably isn't what you want here.

AFFECTSRootCause

I'm trying to receive a nontrivial query parameter object. — since objects seem to be assumed to arrive in the body in `fastapi`. Tension: I've had to do something like this on the server. Outcome: then `model_validate_json` it to get your `MyParam` object.

AFFECTSRootCause

payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM]) — if "authorization" in request.headers. Outcome: create_access_token(.

AFFECTSRootCause

if the function declares the input parameter with `Annotated` and `Depends` — a simple API created in python with FastApi. Tension: the test fails. Outcome: The route responds with a 422 Unprocessable Entity status code.

AFFECTSRootCause

DeprecationWarning: The 'app' shortcut is now deprecated. — when I create the test client.

AFFECTSRootCause

it is always assigned the last value given in the for loop — using the same `model` reference for every endpoint created. Outcome: the issue lies in the fact that you are using the same `model` reference for every endpoint created.

AFFECTSRootCause

Incorrect Cognito region or client configuration prevents the library from finding the matching JWK for the access token

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