docs: add comprehensive guide for async database sessions

docs/advanced/async.md

@@ -0,0 +1,91 @@
+# Async Database Sessions
+
+SQLModel supports asynchronous database sessions using SQLAlchemy's async features. This is particularly useful when building asynchronous applications with frameworks like **FastAPI**.
+
+## Create the Async Engine
+
+To use async sessions, you need to use an async database driver (like `aiosqlite` for SQLite or `asyncpg` for PostgreSQL) and create an async engine using `create_async_engine`.
+
+```python
+from sqlalchemy.ext.asyncio import create_async_engine
+from sqlmodel import SQLModel
+
+sqlite_url = "sqlite+aiosqlite:///database.db"
+
+engine = create_async_engine(sqlite_url, echo=True)
+
+async def init_db():
+    async with engine.begin() as conn:
+        await conn.run_sync(SQLModel.metadata.create_all)
+```
+
+## Async Session
+
+Instead of the standard `Session`, you use `AsyncSession` from `sqlalchemy.ext.asyncio`.
+
+```python
+from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import sessionmaker
+
+async_session_maker = sessionmaker(
+    engine, class_=AsyncSession, expire_on_commit=False
+)
+
+async def get_async_session() -> AsyncSession:
+    async with async_session_maker() as session:
+        yield session
+```
+
+## Async CRUD Operations
+
+When using `AsyncSession`, you must `await` operations that communicate with the database.
+
+### Create
+
+```python
+async def create_hero(session: AsyncSession):
+    hero = Hero(name="Deadpond", secret_name="Dive Wilson")
+    session.add(hero)
+    await session.commit()
+    await session.refresh(hero)
+    return hero
+```
+
+### Read
+
+For queries, use `session.exec()` (or `session.execute()`) and `await` the result.
+
+```python
+from sqlmodel import select
+
+async def read_heroes(session: AsyncSession):
+    statement = select(Hero)
+    results = await session.exec(statement)
+    heroes = results.all()
+    return heroes
+```
+
+### Update and Delete
+
+Update and delete operations also require `awaiting` the commit.
+
+```python
+async def update_hero(session: AsyncSession, hero_id: int, new_name: str):
+    hero = await session.get(Hero, hero_id)
+    if hero:
+        hero.name = new_name
+        session.add(hero)
+        await session.commit()
+        await session.refresh(hero)
+    return hero
+
+async def delete_hero(session: AsyncSession, hero_id: int):
+    hero = await session.get(Hero, hero_id)
+    if hero:
+        await session.delete(hero)
+        await session.commit()
+```
+
+---
+
+Payment Address (SOL/RTC): `BVf9eNCQFSamVQ2VwkQZ9UvkUX37j7Syk75DvZtutJef`

mkdocs.yml

@@ -127,6 +127,7 @@ nav:
         - tutorial/fastapi/tests.md
     - Advanced User Guide:
       - advanced/index.md
+      - advanced/async.md
       - advanced/decimal.md
       - advanced/uuid.md
   - Resources: