Final touches and recap

There is one more improvement that we can make to our application. Currently, we utilize both the SQLAlchemyInitPlugin and the SQLAlchemySerializationPlugin, but there is a shortcut for this configuration: the SQLAlchemyPlugin is a combination of the two, so we can simplify our configuration by using it instead.

Here is our final application:

 1from collections.abc import AsyncGenerator
 2from typing import Optional
 3
 4from sqlalchemy import select
 5from sqlalchemy.exc import IntegrityError, NoResultFound
 6from sqlalchemy.ext.asyncio import AsyncSession
 7from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column
 8
 9from litestar import Litestar, get, post, put
10from litestar.contrib.sqlalchemy.plugins import SQLAlchemyAsyncConfig, SQLAlchemyPlugin
11from litestar.exceptions import ClientException, NotFoundException
12from litestar.status_codes import HTTP_409_CONFLICT
13
14
15class Base(DeclarativeBase): ...
16
17
18class TodoItem(Base):
19    __tablename__ = "todo_items"
20
21    title: Mapped[str] = mapped_column(primary_key=True)
22    done: Mapped[bool]
23
24
25async def provide_transaction(db_session: AsyncSession) -> AsyncGenerator[AsyncSession, None]:
26    try:
27        async with db_session.begin():
28            yield db_session
29    except IntegrityError as exc:
30        raise ClientException(
31            status_code=HTTP_409_CONFLICT,
32            detail=str(exc),
33        ) from exc
34
35
36async def get_todo_by_title(todo_name, session: AsyncSession) -> TodoItem:
37    query = select(TodoItem).where(TodoItem.title == todo_name)
38    result = await session.execute(query)
39    try:
40        return result.scalar_one()
41    except NoResultFound as e:
42        raise NotFoundException(detail=f"TODO {todo_name!r} not found") from e
43
44
45async def get_todo_list(done: Optional[bool], session: AsyncSession) -> list[TodoItem]:
46    query = select(TodoItem)
47    if done is not None:
48        query = query.where(TodoItem.done.is_(done))
49
50    result = await session.execute(query)
51    return result.scalars().all()
52
53
54@get("/")
55async def get_list(transaction: AsyncSession, done: Optional[bool] = None) -> list[TodoItem]:
56    return await get_todo_list(done, transaction)
57
58
59@post("/")
60async def add_item(data: TodoItem, transaction: AsyncSession) -> TodoItem:
61    transaction.add(data)
62    return data
63
64
65@put("/{item_title:str}")
66async def update_item(item_title: str, data: TodoItem, transaction: AsyncSession) -> TodoItem:
67    todo_item = await get_todo_by_title(item_title, transaction)
68    todo_item.title = data.title
69    todo_item.done = data.done
70    return todo_item
71
72
73db_config = SQLAlchemyAsyncConfig(
74    connection_string="sqlite+aiosqlite:///todo.sqlite",
75    metadata=Base.metadata,
76    create_all=True,
77    before_send_handler="autocommit",
78)
79
80app = Litestar(
81    [get_list, add_item, update_item],
82    dependencies={"transaction": provide_transaction},
83    plugins=[SQLAlchemyPlugin(db_config)],
84)

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

Recap

In this tutorial, we have learned how to use the SQLAlchemy plugin to create a simple application that uses a database to store and retrieve data.

In the final application TodoItem is defined, representing a TODO item. It extends from the DeclarativeBase class provided by SQLAlchemy:

1class Base(DeclarativeBase): ...
2
3
4class TodoItem(Base):
5    __tablename__ = "todo_items"
6
7    title: Mapped[str] = mapped_column(primary_key=True)
8    done: Mapped[bool]

Next, we define a dependency that centralizes our database transaction management and error handling. This dependency depends on the db_session dependency, which is provided by the SQLAlchemy plugin, and is made available to our handlers via the transaction argument:

1async def provide_transaction(db_session: AsyncSession) -> AsyncGenerator[AsyncSession, None]:
2    try:
3        async with db_session.begin():
4            yield db_session
5    except IntegrityError as exc:
6        raise ClientException(
7            status_code=HTTP_409_CONFLICT,
8            detail=str(exc),
9        ) from exc

We also define a couple of utility functions, that help us to retrieve our TODO items from the database:

 1async def get_todo_by_title(todo_name, session: AsyncSession) -> TodoItem:
 2    query = select(TodoItem).where(TodoItem.title == todo_name)
 3    result = await session.execute(query)
 4    try:
 5        return result.scalar_one()
 6    except NoResultFound as e:
 7        raise NotFoundException(detail=f"TODO {todo_name!r} not found") from e
 8
 9
10async def get_todo_list(done: Optional[bool], session: AsyncSession) -> list[TodoItem]:
11    query = select(TodoItem)
12    if done is not None:
13        query = query.where(TodoItem.done.is_(done))
14
15    result = await session.execute(query)
16    return result.scalars().all()

We define our route handlers, which are the interface through which TODO items can be created, retrieved and updated:

 1@get("/")
 2async def get_list(transaction: AsyncSession, done: Optional[bool] = None) -> list[TodoItem]:
 3    return await get_todo_list(done, transaction)
 4
 5
 6@post("/")
 7async def add_item(data: TodoItem, transaction: AsyncSession) -> TodoItem:
 8    transaction.add(data)
 9    return data
10
11
12@put("/{item_title:str}")
13async def update_item(item_title: str, data: TodoItem, transaction: AsyncSession) -> TodoItem:
14    todo_item = await get_todo_by_title(item_title, transaction)
15    todo_item.title = data.title
16    todo_item.done = data.done
17    return todo_item

Finally, we define our application, using the SQLAlchemyPlugin to configure SQLAlchemy and manage the engine and session lifecycle, and register our transaction dependency.

1app = Litestar(
2    [get_list, add_item, update_item],
3    dependencies={"transaction": provide_transaction},
4    plugins=[SQLAlchemyPlugin(db_config)],

See also