Page deck and card lists by id with limit and after (#73)

Author: lesnik512

AGENTS.md

@@ -44,9 +44,9 @@ class ListDecksUseCase:
     decks_repository: DecksRepository
 
     @postgres_retry
-    async def __call__(self) -> Sequence[models.Deck]:
+    async def __call__(self, *, after: int | None, limit: int) -> Sequence[models.Deck]:
         async with self.transaction:
-            decks: typing.Final = await self.decks_repository.get_many()
+            decks: typing.Final = await self.decks_repository.list_decks(after=after, limit=limit)
             await self.transaction.commit()
         return decks
 ```
@@ -69,7 +69,8 @@ class ListDecksUseCase:
 ## Conventions
 
 - Routes live in `app/api/`, one module per resource (`decks.py`, `cards.py`), each exposing its own `ROUTER` (`litestar.Router`, prefix `/api`). `application.build_app` registers them all via `route_handlers=[decks.ROUTER, cards.ROUTER]`. Add a new resource by creating `app/api/<name>.py`, defining handlers + a `ROUTER`, and adding it to that list. Its database work goes in `app/use_cases/` with a provider in `ioc.UseCases`.
-- Pydantic schemas in `app/schemas.py` use `from_attributes=True` (via `Base`) so they validate directly from ORM instances (`schemas.X.model_validate(orm_instance)`). Collection responses go through `Collection[T].from_models(...)` (e.g. `schemas.Decks`, `schemas.Cards`).
+- Pydantic schemas in `app/schemas.py` use `from_attributes=True` (via `Base`) so they validate directly from ORM instances (`schemas.X.model_validate(orm_instance)`). Collection responses go through `Collection[T].from_models(...)` (e.g. `schemas.Cards`).
+- List endpoints page by id (keyset). They take `limit` (1 to `schemas.MAX_PAGE_LIMIT`, default `schemas.DEFAULT_PAGE_LIMIT`) and `after`, the last id the client has seen, and return a `Page[T]` subclass (`schemas.DecksPage`, `schemas.CardsPage`) with `items` and `next_after`. The repository filters `id > after` and fetches `limit + 1` rows ordered by id. `Page.from_models(rows, limit=limit)` drops the extra row and sets `next_after` to the last returned id when that row existed, or `null` on the last page. Don't page with OFFSET: Postgres reads and discards every skipped row.
 - Deck responses are deliberately two-shaped: `list_decks`/`create_deck`/`update_deck` return the light `schemas.Deck` (no `cards`), while `get_deck` returns `schemas.DeckWithCards`. The split mirrors loading — lists use `noload` (no cards query), detail uses `joinedload` via `fetch_with_cards` — so the type states exactly what each endpoint loads.
 - Domain exceptions: register handlers in `application.build_app`'s `exception_handlers` dict (`DuplicateKeyError` → `exceptions.duplicate_key_error_handler` returns 400, `NotFoundError` → `exceptions.not_found_error_handler` returns 404). Handlers don't raise HTTP errors themselves: a missing row surfaces as advanced-alchemy's `NotFoundError`.
 - `ruff` is configured with `select = ["ALL"]` and a line length of 120 — expect strict lint. `app/resources/` is exempt from the `TC` rules because modern-di resolves DI creator annotations at runtime. Type-check with `ty`; suppressions already exist for `invalid-argument-type` around `LifespanManager` / `ASGITransport` in `tests/conftest.py`.

app/api/cards.py

@@ -1,8 +1,9 @@
 import typing
+from typing import Annotated
 
 import litestar
 from litestar.di import NamedDependency
-from litestar.params import FromPath
+from litestar.params import FromPath, QueryParameter
 
 from app import schemas
 from app.use_cases.create_cards import CreateCardsUseCase
@@ -12,8 +13,14 @@
 
 
 @litestar.get("/decks/{deck_id:int}/cards/")
-async def list_cards(deck_id: FromPath[int], list_cards_use_case: NamedDependency[ListCardsUseCase]) -> schemas.Cards:
-    return schemas.Cards.from_models(await list_cards_use_case(deck_id=deck_id))
+async def list_cards(
+    deck_id: FromPath[int],
+    list_cards_use_case: NamedDependency[ListCardsUseCase],
+    after: Annotated[int | None, QueryParameter(gt=0)] = None,
+    limit: Annotated[int, QueryParameter(ge=1, le=schemas.MAX_PAGE_LIMIT)] = schemas.DEFAULT_PAGE_LIMIT,
+) -> schemas.CardsPage:
+    cards: typing.Final = await list_cards_use_case(deck_id=deck_id, after=after, limit=limit)
+    return schemas.CardsPage.from_models(cards, limit=limit)
 
 
 @litestar.get("/cards/{card_id:int}/")

app/api/decks.py

@@ -1,8 +1,9 @@
 import typing
+from typing import Annotated
 
 import litestar
 from litestar.di import NamedDependency
-from litestar.params import FromPath
+from litestar.params import FromPath, QueryParameter
 
 from app import schemas
 from app.use_cases.create_deck import CreateDeckUseCase
@@ -12,8 +13,13 @@
 
 
 @litestar.get("/decks/")
-async def list_decks(list_decks_use_case: NamedDependency[ListDecksUseCase]) -> schemas.Decks:
-    return schemas.Decks.from_models(await list_decks_use_case())
+async def list_decks(
+    list_decks_use_case: NamedDependency[ListDecksUseCase],
+    after: Annotated[int | None, QueryParameter(gt=0)] = None,
+    limit: Annotated[int, QueryParameter(ge=1, le=schemas.MAX_PAGE_LIMIT)] = schemas.DEFAULT_PAGE_LIMIT,
+) -> schemas.DecksPage:
+    decks: typing.Final = await list_decks_use_case(after=after, limit=limit)
+    return schemas.DecksPage.from_models(decks, limit=limit)
 
 
 @litestar.get("/decks/{deck_id:int}/")

app/repositories.py

@@ -4,6 +4,7 @@
 
 import sqlalchemy as sa
 from advanced_alchemy.exceptions import NotFoundError, wrap_sqlalchemy_exception
+from advanced_alchemy.filters import LimitOffset
 from advanced_alchemy.repository import DEFAULT_ERROR_MESSAGE_TEMPLATES, SQLAlchemyAsyncRepository
 from advanced_alchemy.service import SQLAlchemyAsyncRepositoryService
 from sqlalchemy import orm
@@ -22,8 +23,12 @@ class BaseRepository(SQLAlchemyAsyncRepository[models.Deck]):
 
     repository_type = BaseRepository
 
-    async def list_decks(self) -> Sequence[models.Deck]:
-        return await self.get_many(order_by=models.Deck.id.asc())
+    async def list_decks(self, *, after: int | None, limit: int) -> Sequence[models.Deck]:
+        return await self.get_many(
+            *([] if after is None else [models.Deck.id > after]),
+            LimitOffset(limit=limit + 1, offset=0),
+            order_by=models.Deck.id.asc(),
+        )
 
     async def get_or_create(self, data: schemas.DeckCreate) -> models.Deck:
         statement = postgresql.insert(models.Deck).values(**data.model_dump())
@@ -56,8 +61,13 @@ class BaseRepository(SQLAlchemyAsyncRepository[models.Card]):
 
     repository_type = BaseRepository
 
-    async def list_for_deck(self, deck_id: int) -> Sequence[models.Card]:
-        return await self.get_many(models.Card.deck_id == deck_id, order_by=models.Card.id.asc())
+    async def list_for_deck(self, deck_id: int, *, after: int | None, limit: int) -> Sequence[models.Card]:
+        return await self.get_many(
+            models.Card.deck_id == deck_id,
+            *([] if after is None else [models.Card.id > after]),
+            LimitOffset(limit=limit + 1, offset=0),
+            order_by=models.Card.id.asc(),
+        )
 
     async def add_cards(self, deck_id: int, cards: list[schemas.CardCreate]) -> Sequence[models.Card]:
         return await self.create_many([models.Card(**card.model_dump(), deck_id=deck_id) for card in cards])

app/schemas.py

@@ -1,12 +1,20 @@
 import uuid
-from typing import TYPE_CHECKING, Self
+from typing import TYPE_CHECKING, Final, Protocol, Self
 
 import pydantic
 from pydantic import BaseModel, PositiveInt
 
 
 if TYPE_CHECKING:
-    from collections.abc import Iterable
+    from collections.abc import Iterable, Sequence
+
+
+DEFAULT_PAGE_LIMIT: Final = 50
+MAX_PAGE_LIMIT: Final = 100
+
+
+class HasId(Protocol):
+    id: int
 
 
 class Base(BaseModel):
@@ -21,6 +29,18 @@ def from_models(cls, objects: Iterable[object]) -> Self:
         return cls.model_validate({"items": list(objects)})
 
 
+class Page[T: Base](Base):
+    items: list[T]
+    next_after: PositiveInt | None
+
+    @classmethod
+    def from_models(cls, objects: Sequence[HasId], *, limit: int) -> Self:
+        has_next: Final = len(objects) > limit
+        return cls.model_validate(
+            {"items": list(objects[:limit]), "next_after": objects[limit - 1].id if has_next else None}
+        )
+
+
 class CardBase(Base):
     front: str
     back: str | None = None
@@ -43,6 +63,10 @@ class Cards(Collection[Card]):
     pass
 
 
+class CardsPage(Page[Card]):
+    pass
+
+
 class DeckBase(Base):
     name: str
     description: str | None = None
@@ -68,5 +92,5 @@ class DeckWithCards(Deck):
     cards: list[Card]
 
 
-class Decks(Collection[Deck]):
+class DecksPage(Page[Deck]):
     pass

app/use_cases/list_cards.py

@@ -14,8 +14,8 @@ class ListCardsUseCase:
     cards_repository: CardsRepository
 
     @postgres_retry
-    async def __call__(self, *, deck_id: int) -> Sequence[models.Card]:
+    async def __call__(self, *, deck_id: int, after: int | None, limit: int) -> Sequence[models.Card]:
         async with self.transaction:
-            cards: typing.Final = await self.cards_repository.list_for_deck(deck_id)
+            cards: typing.Final = await self.cards_repository.list_for_deck(deck_id, after=after, limit=limit)
             await self.transaction.commit()
         return cards

app/use_cases/list_decks.py

@@ -14,8 +14,8 @@ class ListDecksUseCase:
     decks_repository: DecksRepository
 
     @postgres_retry
-    async def __call__(self) -> Sequence[models.Deck]:
+    async def __call__(self, *, after: int | None, limit: int) -> Sequence[models.Deck]:
         async with self.transaction:
-            decks: typing.Final = await self.decks_repository.list_decks()
+            decks: typing.Final = await self.decks_repository.list_decks(after=after, limit=limit)
             await self.transaction.commit()
         return decks

tests/test_cards.py

@@ -70,7 +70,7 @@ async def test_create_cards(client: AsyncClient) -> None:
     response = await client.get(f"/api/decks/{deck.id}/cards/")
     assert response.status_code == status_codes.HTTP_200_OK
     data = response.json()
-    assert created_data == data
+    assert created_data["items"] == data["items"]
     assert len(data["items"]) == len(cards_to_create)
     for k, v in cards_to_create[0].model_dump().items():
         assert data["items"][0][k] == v
@@ -188,3 +188,30 @@ async def test_update_cards_to_a_duplicate_front(client: AsyncClient) -> None:
 
     response = await client.put(f"/api/decks/{deck.id}/cards/", json=[{"id": card2.id, "front": card1.front}])
     assert response.status_code == status_codes.HTTP_400_BAD_REQUEST
+
+
+async def test_list_cards_pages_by_id_within_deck(client: AsyncClient) -> None:
+    deck, other_deck = await factories.DeckModelFactory.create_batch_async(size=2)
+    first, second = await factories.CardModelFactory.create_batch_async(size=2, deck_id=deck.id)
+    await factories.CardModelFactory.create_async(deck_id=other_deck.id)
+    third = await factories.CardModelFactory.create_async(deck_id=deck.id)
+
+    response = await client.get(f"/api/decks/{deck.id}/cards/", params={"limit": 2})
+    assert response.status_code == status_codes.HTTP_200_OK
+    data = response.json()
+    assert [x["id"] for x in data["items"]] == [first.id, second.id]
+    assert data["next_after"] == second.id
+
+    response = await client.get(f"/api/decks/{deck.id}/cards/", params={"limit": 2, "after": data["next_after"]})
+    assert response.status_code == status_codes.HTTP_200_OK
+    data = response.json()
+    assert [x["id"] for x in data["items"]] == [third.id]
+    assert data["next_after"] is None
+
+
+@pytest.mark.parametrize("params", [{"limit": 0}, {"limit": 101}, {"after": 0}])
+async def test_list_cards_rejects_bad_page_params(client: AsyncClient, params: dict[str, int | str]) -> None:
+    deck = await factories.DeckModelFactory.create_async()
+
+    response = await client.get(f"/api/decks/{deck.id}/cards/", params=params)
+    assert response.status_code == status_codes.HTTP_400_BAD_REQUEST

tests/test_decks.py

@@ -204,3 +204,49 @@ async def test_put_decks_moves_updated_at(client: AsyncClient, db_session: Async
     assert response.status_code == status_codes.HTTP_200_OK
     updated_at = (await db_session.scalars(sa.select(models.Deck.updated_at).where(models.Deck.id == deck.id))).one()
     assert updated_at > long_ago
+
+
+async def test_list_decks_first_page(client: AsyncClient) -> None:
+    decks = await factories.DeckModelFactory.create_batch_async(size=3)
+
+    response = await client.get("/api/decks/", params={"limit": 2})
+    assert response.status_code == status_codes.HTTP_200_OK
+    data = response.json()
+    assert [x["id"] for x in data["items"]] == [decks[0].id, decks[1].id]
+    assert data["next_after"] == decks[1].id
+
+
+async def test_list_decks_after_cursor(client: AsyncClient) -> None:
+    decks = await factories.DeckModelFactory.create_batch_async(size=3)
+
+    response = await client.get("/api/decks/", params={"limit": 2, "after": decks[1].id})
+    assert response.status_code == status_codes.HTTP_200_OK
+    data = response.json()
+    assert [x["id"] for x in data["items"]] == [decks[2].id]
+    assert data["next_after"] is None
+
+
+async def test_list_decks_exactly_limit_has_no_next_page(client: AsyncClient) -> None:
+    decks = await factories.DeckModelFactory.create_batch_async(size=2)
+
+    response = await client.get("/api/decks/", params={"limit": 2})
+    assert response.status_code == status_codes.HTTP_200_OK
+    data = response.json()
+    assert [x["id"] for x in data["items"]] == [x.id for x in decks]
+    assert data["next_after"] is None
+
+
+async def test_list_decks_default_limit(client: AsyncClient) -> None:
+    decks = await factories.DeckModelFactory.create_batch_async(size=51)
+
+    response = await client.get("/api/decks/")
+    assert response.status_code == status_codes.HTTP_200_OK
+    data = response.json()
+    assert [x["id"] for x in data["items"]] == [x.id for x in decks[:50]]
+    assert data["next_after"] == decks[49].id
+
+
+@pytest.mark.parametrize("params", [{"limit": 0}, {"limit": 101}, {"after": 0}, {"after": "x"}])
+async def test_list_decks_rejects_bad_page_params(client: AsyncClient, params: dict[str, int | str]) -> None:
+    response = await client.get("/api/decks/", params=params)
+    assert response.status_code == status_codes.HTTP_400_BAD_REQUEST