feat: unified paginate() endpoint with typed pagination responses (#134)

* feat: unified paginate() endpoint with typed pagination responses

* docs: unified paginate() endpoint

* fix: add tests

src/fastapi_toolsets/crud/__init__.py

@@ -1,6 +1,7 @@
 """Generic async CRUD operations for SQLAlchemy models."""
 
 from ..exceptions import InvalidFacetFilterError, NoSearchableFieldsError
+from ..schemas import PaginationType
 from ..types import (
     FacetFieldType,
     JoinType,
@@ -8,10 +9,11 @@ from ..types import (
     OrderByClause,
     SearchFieldType,
 )
-from .factory import CrudFactory
+from .factory import AsyncCrud, CrudFactory
 from .search import SearchConfig, get_searchable_fields
 
 __all__ = [
+    "AsyncCrud",
     "CrudFactory",
     "FacetFieldType",
     "get_searchable_fields",
@@ -20,6 +22,7 @@ __all__ = [
     "M2MFieldType",
     "NoSearchableFieldsError",
     "OrderByClause",
+    "PaginationType",
     "SearchConfig",
     "SearchFieldType",
 ]

src/fastapi_toolsets/crud/factory.py

@@ -23,7 +23,14 @@ from sqlalchemy.sql.roles import WhereHavingRole
 
 from ..db import get_transaction
 from ..exceptions import InvalidOrderFieldError, NotFoundError
-from ..schemas import CursorPagination, OffsetPagination, PaginatedResponse, Response
+from ..schemas import (
+    CursorPaginatedResponse,
+    CursorPagination,
+    OffsetPaginatedResponse,
+    OffsetPagination,
+    PaginationType,
+    Response,
+)
 from ..types import (
     FacetFieldType,
     JoinType,
@@ -892,7 +899,7 @@ class AsyncCrud(Generic[ModelType]):
         facet_fields: Sequence[FacetFieldType] | None = None,
         filter_by: dict[str, Any] | BaseModel | None = None,
         schema: type[BaseModel],
-    ) -> PaginatedResponse[Any]:
+    ) -> OffsetPaginatedResponse[Any]:
         """Get paginated results using offset-based pagination.
 
         Args:
@@ -974,7 +981,7 @@ class AsyncCrud(Generic[ModelType]):
             session, facet_fields, filters, search_joins
         )
 
-        return PaginatedResponse(
+        return OffsetPaginatedResponse(
             data=items,
             pagination=OffsetPagination(
                 total_count=total_count,
@@ -1002,7 +1009,7 @@ class AsyncCrud(Generic[ModelType]):
         facet_fields: Sequence[FacetFieldType] | None = None,
         filter_by: dict[str, Any] | BaseModel | None = None,
         schema: type[BaseModel],
-    ) -> PaginatedResponse[Any]:
+    ) -> CursorPaginatedResponse[Any]:
         """Get paginated results using cursor-based pagination.
 
         Args:
@@ -1142,7 +1149,7 @@ class AsyncCrud(Generic[ModelType]):
             session, facet_fields, filters, search_joins
         )
 
-        return PaginatedResponse(
+        return CursorPaginatedResponse(
             data=items,
             pagination=CursorPagination(
                 next_cursor=next_cursor,
@@ -1153,6 +1160,144 @@ class AsyncCrud(Generic[ModelType]):
             filter_attributes=filter_attributes,
         )
 
+    @overload
+    @classmethod
+    async def paginate(  # pragma: no cover
+        cls: type[Self],
+        session: AsyncSession,
+        *,
+        pagination_type: Literal[PaginationType.OFFSET],
+        filters: list[Any] | None = ...,
+        joins: JoinType | None = ...,
+        outer_join: bool = ...,
+        load_options: Sequence[ExecutableOption] | None = ...,
+        order_by: OrderByClause | None = ...,
+        page: int = ...,
+        cursor: str | None = ...,
+        items_per_page: int = ...,
+        search: str | SearchConfig | None = ...,
+        search_fields: Sequence[SearchFieldType] | None = ...,
+        facet_fields: Sequence[FacetFieldType] | None = ...,
+        filter_by: dict[str, Any] | BaseModel | None = ...,
+        schema: type[BaseModel],
+    ) -> OffsetPaginatedResponse[Any]: ...
+
+    @overload
+    @classmethod
+    async def paginate(  # pragma: no cover
+        cls: type[Self],
+        session: AsyncSession,
+        *,
+        pagination_type: Literal[PaginationType.CURSOR],
+        filters: list[Any] | None = ...,
+        joins: JoinType | None = ...,
+        outer_join: bool = ...,
+        load_options: Sequence[ExecutableOption] | None = ...,
+        order_by: OrderByClause | None = ...,
+        page: int = ...,
+        cursor: str | None = ...,
+        items_per_page: int = ...,
+        search: str | SearchConfig | None = ...,
+        search_fields: Sequence[SearchFieldType] | None = ...,
+        facet_fields: Sequence[FacetFieldType] | None = ...,
+        filter_by: dict[str, Any] | BaseModel | None = ...,
+        schema: type[BaseModel],
+    ) -> CursorPaginatedResponse[Any]: ...
+
+    @classmethod
+    async def paginate(
+        cls: type[Self],
+        session: AsyncSession,
+        *,
+        pagination_type: PaginationType = PaginationType.OFFSET,
+        filters: list[Any] | None = None,
+        joins: JoinType | None = None,
+        outer_join: bool = False,
+        load_options: Sequence[ExecutableOption] | None = None,
+        order_by: OrderByClause | None = None,
+        page: int = 1,
+        cursor: str | None = None,
+        items_per_page: int = 20,
+        search: str | SearchConfig | None = None,
+        search_fields: Sequence[SearchFieldType] | None = None,
+        facet_fields: Sequence[FacetFieldType] | None = None,
+        filter_by: dict[str, Any] | BaseModel | None = None,
+        schema: type[BaseModel],
+    ) -> OffsetPaginatedResponse[Any] | CursorPaginatedResponse[Any]:
+        """Get paginated results using either offset or cursor pagination.
+
+        Args:
+            session: DB async session.
+            pagination_type: Pagination strategy.  Defaults to
+                ``PaginationType.OFFSET``.
+            filters: List of SQLAlchemy filter conditions.
+            joins: List of ``(model, condition)`` tuples for joining related
+                tables.
+            outer_join: Use LEFT OUTER JOIN instead of INNER JOIN.
+            load_options: SQLAlchemy loader options.  Falls back to
+                ``default_load_options`` when not provided.
+            order_by: Column or expression to order results by.
+            page: Page number (1-indexed).  Only used when
+                ``pagination_type`` is ``OFFSET``.
+            cursor: Cursor token from a previous
+                :class:`.CursorPaginatedResponse`.  Only used when
+                ``pagination_type`` is ``CURSOR``.
+            items_per_page: Number of items per page (default 20).
+            search: Search query string or :class:`.SearchConfig` object.
+            search_fields: Fields to search in (overrides class default).
+            facet_fields: Columns to compute distinct values for (overrides
+                class default).
+            filter_by: Dict of ``{column_key: value}`` to filter by declared
+                facet fields.  Keys must match the ``column.key`` of a facet
+                field.  Scalar → equality, list → IN clause.  Raises
+                :exc:`.InvalidFacetFilterError` for unknown keys.
+            schema: Pydantic schema to serialize each item into.
+
+        Returns:
+            :class:`.OffsetPaginatedResponse` when ``pagination_type`` is
+            ``OFFSET``, :class:`.CursorPaginatedResponse` when it is
+            ``CURSOR``.
+        """
+        if items_per_page < 1:
+            raise ValueError(f"items_per_page must be >= 1, got {items_per_page}")
+        match pagination_type:
+            case PaginationType.CURSOR:
+                return await cls.cursor_paginate(
+                    session,
+                    cursor=cursor,
+                    filters=filters,
+                    joins=joins,
+                    outer_join=outer_join,
+                    load_options=load_options,
+                    order_by=order_by,
+                    items_per_page=items_per_page,
+                    search=search,
+                    search_fields=search_fields,
+                    facet_fields=facet_fields,
+                    filter_by=filter_by,
+                    schema=schema,
+                )
+            case PaginationType.OFFSET:
+                if page < 1:
+                    raise ValueError(f"page must be >= 1, got {page}")
+                return await cls.offset_paginate(
+                    session,
+                    filters=filters,
+                    joins=joins,
+                    outer_join=outer_join,
+                    load_options=load_options,
+                    order_by=order_by,
+                    page=page,
+                    items_per_page=items_per_page,
+                    search=search,
+                    search_fields=search_fields,
+                    facet_fields=facet_fields,
+                    filter_by=filter_by,
+                    schema=schema,
+                )
+            case _:
+                raise ValueError(f"Unknown pagination_type: {pagination_type!r}")
+
 
 def CrudFactory(
     model: type[ModelType],

src/fastapi_toolsets/schemas.py

@@ -1,7 +1,7 @@
 """Base Pydantic schemas for API responses."""
 
 from enum import Enum
-from typing import Any, ClassVar, Generic
+from typing import Any, ClassVar, Generic, Literal
 
 from pydantic import BaseModel, ConfigDict
 
@@ -10,9 +10,12 @@ from .types import DataT
 __all__ = [
     "ApiError",
     "CursorPagination",
+    "CursorPaginatedResponse",
     "ErrorResponse",
     "OffsetPagination",
+    "OffsetPaginatedResponse",
     "PaginatedResponse",
+    "PaginationType",
     "PydanticBase",
     "Response",
     "ResponseStatus",
@@ -123,9 +126,48 @@ class CursorPagination(PydanticBase):
     has_more: bool
 
 
+class PaginationType(str, Enum):
+    """Pagination strategy selector for :meth:`.AsyncCrud.paginate`."""
+
+    OFFSET = "offset"
+    CURSOR = "cursor"
+
+
 class PaginatedResponse(BaseResponse, Generic[DataT]):
-    """Paginated API response for list endpoints."""
+    """Paginated API response for list endpoints.
+
+    Base class and return type for endpoints that support both pagination
+    strategies.  Use :class:`OffsetPaginatedResponse` or
+    :class:`CursorPaginatedResponse` when the strategy is fixed;  use
+    ``PaginatedResponse`` as the return annotation for unified endpoints that
+    dispatch via :meth:`~fastapi_toolsets.crud.factory.AsyncCrud.paginate`.
+    """
 
     data: list[DataT]
     pagination: OffsetPagination | CursorPagination
+    pagination_type: PaginationType | None = None
     filter_attributes: dict[str, list[Any]] | None = None
+
+
+class OffsetPaginatedResponse(PaginatedResponse[DataT]):
+    """Paginated response with typed offset-based pagination metadata.
+
+    The ``pagination_type`` field is always ``"offset"`` and acts as a
+    discriminator, allowing frontend clients to narrow the union type returned
+    by a unified ``paginate()`` endpoint.
+    """
+
+    pagination: OffsetPagination
+    pagination_type: Literal[PaginationType.OFFSET] = PaginationType.OFFSET
+
+
+class CursorPaginatedResponse(PaginatedResponse[DataT]):
+    """Paginated response with typed cursor-based pagination metadata.
+
+    The ``pagination_type`` field is always ``"cursor"`` and acts as a
+    discriminator, allowing frontend clients to narrow the union type returned
+    by a unified ``paginate()`` endpoint.
+    """
+
+    pagination: CursorPagination
+    pagination_type: Literal[PaginationType.CURSOR] = PaginationType.CURSOR