Fix issue with pydantic v2 params validation (#781)

Author: uriyyo

fastapi_pagination/api.py

@@ -37,11 +37,12 @@
     lenient_issubclass,
 )
 from fastapi.routing import APIRoute, APIRouter
+from pydantic import BaseModel
 
 from .bases import AbstractPage, AbstractParams
 from .default import Page
 from .types import AsyncItemsTransformer, ItemsTransformer, SyncItemsTransformer
-from .utils import is_async_callable
+from .utils import IS_PYDANTIC_V2, is_async_callable
 
 T = TypeVar("T")
 TAbstractParams = TypeVar("TAbstractParams", covariant=True, bound=AbstractParams)
@@ -245,7 +246,18 @@ async def _pagination_params(*args: Any, **kwargs: Any) -> AsyncIterator[TAbstra
         with _ctx_var_with_reset(_params_val, cast(AbstractParams, val)):
             yield val
 
-    _pagination_params.__signature__ = inspect.signature(params)  # type: ignore[attr-defined]
+    sign = inspect.signature(params)
+
+    if IS_PYDANTIC_V2:
+        with suppress(ValueError, TypeError):
+            if issubclass(params, BaseModel):
+                sign_params = {**sign.parameters}
+                for name, field in params.model_fields.items():
+                    sign_params[name] = sign_params[name].replace(default=field)
+
+                sign = sign.replace(parameters=[*sign_params.values()])
+
+    _pagination_params.__signature__ = sign  # type: ignore[attr-defined]
 
     return _pagination_params
 

tests/test_api.py

@@ -1,6 +1,6 @@
 from typing import Any, Generic, Sequence, TypeVar
 
-from fastapi import Depends, FastAPI, Request, Response
+from fastapi import Depends, FastAPI, Request, Response, status
 from fastapi.routing import APIRouter
 from fastapi.testclient import TestClient
 from pydantic import Field
@@ -235,3 +235,20 @@ async def async_transformer(items):
         match=r"^apply_items_transformer called with async_=False but transformer is async$",
     ):
         apply_items_transformer([], async_transformer, async_=False)
+
+
+def test_no_exception_on_validation_error():
+    app = FastAPI()
+    client = TestClient(app)
+
+    @app.get(
+        "/",
+        response_model=Page[int],
+    )
+    async def route():
+        return paginate([])
+
+    add_pagination(app)
+
+    rsp = client.get("/", params={"page": -1})
+    assert rsp.status_code == status.HTTP_422_UNPROCESSABLE_ENTITY