Using the serialization plugin

Our next improvement is to leverage the SQLAlchemySerializationPlugin so that we can receive and return our SQLAlchemy models directly to and from our handlers.

Here’s the code:

 1from collections.abc import AsyncGenerator
 2from contextlib import asynccontextmanager
 3
 4from advanced_alchemy.extensions.litestar import SQLAlchemySerializationPlugin
 5from sqlalchemy import select
 6from sqlalchemy.exc import IntegrityError, NoResultFound
 7from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 8from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
 9
10from litestar import Litestar, get, post, put
11from litestar.datastructures import State
12from litestar.exceptions import ClientException, NotFoundException
13from litestar.status_codes import HTTP_409_CONFLICT
14
15
16class Base(DeclarativeBase): ...
17
18
19class TodoItem(Base):
20    __tablename__ = "todo_items"
21
22    title: Mapped[str] = mapped_column(primary_key=True)
23    done: Mapped[bool]
24
25
26@asynccontextmanager
27async def db_connection(app: Litestar) -> AsyncGenerator[None, None]:
28    engine = getattr(app.state, "engine", None)
29    if engine is None:
30        engine = create_async_engine("sqlite+aiosqlite:///todo.sqlite", echo=True)
31        app.state.engine = engine
32
33    async with engine.begin() as conn:
34        await conn.run_sync(Base.metadata.create_all)
35
36    try:
37        yield
38    finally:
39        await engine.dispose()
40
41
42sessionmaker = async_sessionmaker(expire_on_commit=False)
43
44
45async def provide_transaction(state: State) -> AsyncGenerator[AsyncSession, None]:
46    async with sessionmaker(bind=state.engine) as session:
47        try:
48            async with session.begin():
49                yield session
50        except IntegrityError as exc:
51            raise ClientException(
52                status_code=HTTP_409_CONFLICT,
53                detail=str(exc),
54            ) from exc
55
56
57async def get_todo_by_title(todo_name: str, session: AsyncSession) -> TodoItem:
58    query = select(TodoItem).where(TodoItem.title == todo_name)
59    result = await session.execute(query)
60    try:
61        return result.scalar_one()
62    except NoResultFound as e:
63        raise NotFoundException(detail=f"TODO {todo_name!r} not found") from e
64
65
66async def get_todo_list(done: bool | None, session: AsyncSession) -> list[TodoItem]:
67    query = select(TodoItem)
68    if done is not None:
69        query = query.where(TodoItem.done.is_(done))
70
71    result = await session.execute(query)
72    return list(result.scalars().all())
73
74
75@get("/")
76async def get_list(transaction: AsyncSession, done: bool | None = None) -> list[TodoItem]:
77    return await get_todo_list(done, transaction)
78
79
80@post("/")
81async def add_item(data: TodoItem, transaction: AsyncSession) -> TodoItem:
82    transaction.add(data)
83    return data
84
85
86@put("/{item_title:str}")
87async def update_item(item_title: str, data: TodoItem, transaction: AsyncSession) -> TodoItem:
88    todo_item = await get_todo_by_title(item_title, transaction)
89    todo_item.title = data.title
90    todo_item.done = data.done
91    return todo_item
92
93
94app = Litestar(
95    [get_list, add_item, update_item],
96    dependencies={"transaction": provide_transaction},
97    lifespan=[db_connection],
98    plugins=[SQLAlchemySerializationPlugin()],
99)

 1from collections.abc import AsyncGenerator
 2from contextlib import asynccontextmanager
 3
 4from advanced_alchemy.extensions.litestar import SQLAlchemySerializationPlugin
 5from sqlalchemy import select
 6from sqlalchemy.exc import IntegrityError, NoResultFound
 7from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 8from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
 9
10from litestar import Litestar, get, post, put
11from litestar.datastructures import State
12from litestar.exceptions import ClientException, NotFoundException
13from litestar.status_codes import HTTP_409_CONFLICT
14
15
16class Base(DeclarativeBase): ...
17
18
19class TodoItem(Base):
20    __tablename__ = "todo_items"
21
22    title: Mapped[str] = mapped_column(primary_key=True)
23    done: Mapped[bool]
24
25
26@asynccontextmanager
27async def db_connection(app: Litestar) -> AsyncGenerator[None]:
28    engine = getattr(app.state, "engine", None)
29    if engine is None:
30        engine = create_async_engine("sqlite+aiosqlite:///todo.sqlite", echo=True)
31        app.state.engine = engine
32
33    async with engine.begin() as conn:
34        await conn.run_sync(Base.metadata.create_all)
35
36    try:
37        yield
38    finally:
39        await engine.dispose()
40
41
42sessionmaker = async_sessionmaker(expire_on_commit=False)
43
44
45async def provide_transaction(state: State) -> AsyncGenerator[AsyncSession]:
46    async with sessionmaker(bind=state.engine) as session:
47        try:
48            async with session.begin():
49                yield session
50        except IntegrityError as exc:
51            raise ClientException(
52                status_code=HTTP_409_CONFLICT,
53                detail=str(exc),
54            ) from exc
55
56
57async def get_todo_by_title(todo_name: str, session: AsyncSession) -> TodoItem:
58    query = select(TodoItem).where(TodoItem.title == todo_name)
59    result = await session.execute(query)
60    try:
61        return result.scalar_one()
62    except NoResultFound as e:
63        raise NotFoundException(detail=f"TODO {todo_name!r} not found") from e
64
65
66async def get_todo_list(done: bool | None, session: AsyncSession) -> list[TodoItem]:
67    query = select(TodoItem)
68    if done is not None:
69        query = query.where(TodoItem.done.is_(done))
70
71    result = await session.execute(query)
72    return list(result.scalars().all())
73
74
75@get("/")
76async def get_list(transaction: AsyncSession, done: bool | None = None) -> list[TodoItem]:
77    return await get_todo_list(done, transaction)
78
79
80@post("/")
81async def add_item(data: TodoItem, transaction: AsyncSession) -> TodoItem:
82    transaction.add(data)
83    return data
84
85
86@put("/{item_title:str}")
87async def update_item(item_title: str, data: TodoItem, transaction: AsyncSession) -> TodoItem:
88    todo_item = await get_todo_by_title(item_title, transaction)
89    todo_item.title = data.title
90    todo_item.done = data.done
91    return todo_item
92
93
94app = Litestar(
95    [get_list, add_item, update_item],
96    dependencies={"transaction": provide_transaction},
97    lifespan=[db_connection],
98    plugins=[SQLAlchemySerializationPlugin()],
99)

We’ve simply imported the plugin and added it to our app’s plugins list, and now we can receive and return our SQLAlchemy data models directly to and from our handler.

We’ve also been able to remove the TodoType and TodoCollectionType aliases, and the serialize_todo() function, making the implementation even more concise.

Compare handlers before and after Serialization Plugin

Once more, let’s compare the sets of application handlers before and after our refactoring:

 1from advanced_alchemy.extensions.litestar import SQLAlchemySerializationPlugin
 2from sqlalchemy.ext.asyncio import AsyncSession
 3
 4from litestar import Litestar, get, post, put
 5
 6
 7@get("/")
 8async def get_list(transaction: AsyncSession, done: bool | None = None) -> list[TodoItem]:
 9    return await get_todo_list(done, transaction)
10
11
12@post("/")
13async def add_item(data: TodoItem, transaction: AsyncSession) -> TodoItem:
14    transaction.add(data)
15    return data
16
17
18@put("/{item_title:str}")
19async def update_item(item_title: str, data: TodoItem, transaction: AsyncSession) -> TodoItem:
20    todo_item = await get_todo_by_title(item_title, transaction)
21    todo_item.title = data.title
22    todo_item.done = data.done
23    return todo_item
24
25
26app = Litestar(
27    [get_list, add_item, update_item],
28    dependencies={"transaction": provide_transaction},
29    lifespan=[db_connection],
30    plugins=[SQLAlchemySerializationPlugin()],
31)

 1from collections.abc import AsyncGenerator, Sequence
 2from contextlib import asynccontextmanager
 3from typing import Any
 4
 5from sqlalchemy import select
 6from sqlalchemy.exc import IntegrityError, NoResultFound
 7from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
 8from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
 9
10from litestar import Litestar, get, post, put
11from litestar.datastructures import State
12from litestar.exceptions import ClientException, NotFoundException
13    return result.scalars().all()
14
15
16@get("/")
17async def get_list(state: State, done: bool | None = None) -> TodoCollectionType:
18    async with sessionmaker(bind=state.engine) as session:
19        return [serialize_todo(todo) for todo in await get_todo_list(done, session)]
20
21
22@post("/")
23async def add_item(data: TodoType, state: State) -> TodoType:
24    new_todo = TodoItem(title=data["title"], done=data["done"])
25    async with sessionmaker(bind=state.engine) as session:
26        try:
27            async with session.begin():
28                session.add(new_todo)
29        except IntegrityError as e:
30            raise ClientException(
31                status_code=HTTP_409_CONFLICT,
32                detail=f"TODO {new_todo.title!r} already exists",
33            ) from e
34
35    return serialize_todo(new_todo)
36
37
38@put("/{item_title:str}")
39async def update_item(item_title: str, data: TodoType, state: State) -> TodoType:
40    async with sessionmaker(bind=state.engine) as session, session.begin():
41        todo_item = await get_todo_by_title(item_title, session)
42        todo_item.title = data["title"]
43        todo_item.done = data["done"]
44    return serialize_todo(todo_item)

Very nice! But, we can do better.

Next steps

In our application, we’ve had to build a bit of scaffolding to integrate SQLAlchemy with our application. We’ve had to define the db_connection() lifespan context manager, and the provide_transaction() dependency provider.

Next we’ll look at how the SQLAlchemyInitPlugin can help us.