feat: Introduce ASYNC DB as Plug and Play (#16)

Co-authored-by: vikbhas <waraa.vignesh@gmail.com>

creyPY/fastapi/pagination.py

@@ -1,5 +1,6 @@
 from math import ceil
-from typing import Any, Generic, Optional, Self, Sequence, TypeVar, Union
+from typing import Any, Generic, Optional, Self, Sequence, TypeVar, Union, overload
+from contextlib import suppress
 from pydantic import BaseModel
 from fastapi_pagination import Params
 from fastapi_pagination.bases import AbstractPage, AbstractParams
@@ -8,6 +9,8 @@ from fastapi_pagination.types import (
     GreaterEqualZero,
     AdditionalData,
     SyncItemsTransformer,
+    AsyncItemsTransformer,
+    ItemsTransformer
 )
 from fastapi_pagination.api import create_page, apply_items_transformer
 from fastapi_pagination.utils import verify_params
@@ -17,7 +20,9 @@ from pydantic.json_schema import SkipJsonSchema
 from sqlalchemy.sql.selectable import Select
 from sqlalchemy.orm.session import Session
 from sqlalchemy import select, func
+from sqlalchemy.ext.asyncio import AsyncSession, async_scoped_session
 from fastapi import Query
+from sqlalchemy.util import await_only, greenlet_spawn
 
 T = TypeVar("T")
 
@@ -107,19 +112,59 @@ def unwrap_scalars(
 ) -> Union[Sequence[T], Sequence[Sequence[T]]]:
     return [item[0] if force_unwrap else item for item in items]
 
+def _get_sync_conn_from_async(conn: Any) -> Session:  # pragma: no cover
+    if isinstance(conn, async_scoped_session):
+        conn = conn()
 
+    with suppress(AttributeError):
+        return conn.sync_session  # type: ignore
+
+    with suppress(AttributeError):
+        return conn.sync_connection  # type: ignore
+
+    raise TypeError("conn must be an AsyncConnection or AsyncSession")
+
+@overload
 def paginate(
     connection: Session,
     query: Select,
     params: Optional[AbstractParams] = None,
     transformer: Optional[SyncItemsTransformer] = None,
     additional_data: Optional[AdditionalData] = None,
+) -> Any:
+    pass
+
+
+@overload
+async def paginate(
+    connection: AsyncSession,
+    query: Select,
+    params: Optional[AbstractParams] = None,
+    transformer: Optional[AsyncItemsTransformer] = None,
+    additional_data: Optional[AdditionalData] = None,
+) -> Any:
+    pass
+
+
+def _paginate(
+    connection: Session,
+    query: Select,
+    params: Optional[AbstractParams] = None,
+    transformer: Optional[ItemsTransformer] = None,
+    additional_data: Optional[AdditionalData] = None,
+    async_:bool = False
 ):
+    
+    if async_:
+        def _apply_items_transformer(*args: Any, **kwargs: Any) -> Any:
+            return await_only(apply_items_transformer(*args, **kwargs, async_=True))
+    else:
+        _apply_items_transformer = apply_items_transformer
 
     params, raw_params = verify_params(params, "limit-offset", "cursor")
     count_query = create_count_query(query)
     total = connection.scalar(count_query)
-
+    
     if params.pagination is False and total > 0:
         params = Params(page=1, size=total)
     else:
@@ -129,7 +174,7 @@ def paginate(
     items = connection.execute(query).all()
 
     items = unwrap_scalars(items)
-    t_items = apply_items_transformer(items, transformer)
+    t_items = _apply_items_transformer(items, transformer)
 
     return create_page(
         t_items,
@@ -137,3 +182,29 @@ def paginate(
         total=total,
         **(additional_data or {}),
     )
+
+def paginate(
+    connection: Session,
+    query: Select,
+    params: Optional[AbstractParams] = None,
+    transformer: Optional[ItemsTransformer] = None,
+    additional_data: Optional[AdditionalData] = None,
+):
+    if isinstance(connection,AsyncSession):
+        connection = _get_sync_conn_from_async(connection)
+        return greenlet_spawn(_paginate,
+                              connection,
+                            query,
+                            params,
+                            transformer,
+                            additional_data,
+                            async_=True)
+
+    return _paginate(
+            connection,
+            query,
+            params,
+            transformer,
+            additional_data,
+            async_=False
+        )