---
description: FastAPI with Pydantic v2 only; no Pydantic v1 models, config or methods
globs: "**/*.py"
alwaysApply: false
---

This FastAPI service uses Pydantic v2. FastAPI refuses `pydantic.v1` models.

| Never (Pydantic v1) | Always (Pydantic v2) |
|---|---|
| `class Config: orm_mode = True` | `model_config = ConfigDict(from_attributes=True)` |
| `@validator("x")` | `@field_validator("x")` + `@classmethod` |
| `@root_validator` | `@model_validator(mode="after")` |
| `m.dict()`, `m.json()` | `m.model_dump()`, `m.model_dump_json()` |
| `M.parse_obj(d)`, `M.from_orm(row)` | `M.model_validate(d)`, `M.model_validate(row)` |
| `m.copy(update=...)` | `m.model_copy(update=...)` |
| `Field(regex=...)`, `Field(min_items=1)` | `Field(pattern=...)`, `Field(min_length=1)` |
| `Field(const=True)` | `Literal["value"]` |
| `from pydantic import BaseSettings` | `from pydantic_settings import BaseSettings` |
| `note: Optional[str]` meaning "may be left out" | `note: str \| None = None` |
| `@app.on_event("startup")` | `FastAPI(lifespan=lifespan)` |

- After editing, run the `pydantic-v2-guard` skill's scanner, then pytest with `-W error::pydantic.warnings.PydanticDeprecatedSince20`.