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FastAPI doesn't require you to use a SQL (relational) database.
But you can use any relational database that you want.
Here we'll see an example using SQLAlchemy.
You can easily adapt it to any database supported by SQLAlchemy, like:
- PostgreSQL
- MySQL
- SQLite
- Oracle
- Microsoft SQL Server, etc.
In this example, we'll use SQLite, because it uses a single file and Python has integrated support. So, you can copy this example and run it as is.
Later, for your production application, you might want to use a database server like PostgreSQL.
!!! note
Notice that most of the code is the standard SQLAlchemy code you would use with any framework.
The **FastAPI** specific code is as small as always.
Import SQLAlchemy components
For now, don't pay attention to the rest, only the imports:
{!./src/sql_databases/tutorial001.py!}
Define the database
Define the database that SQLAlchemy should "connect" to:
{!./src/sql_databases/tutorial001.py!}
In this example, we are "connecting" to a SQLite database (opening a file with the SQLite database).
The file will be located at the same directory in the file test.db. That's why the last part is ./test.db.
If you were using a PostgreSQL database instead, you would just have to uncomment the line:
SQLALCHEMY_DATABASE_URI = "postgresql://user:password@postgresserver/db"
...and adapt it with your database data and credentials (equivalently for MySQL, MariaDB or any other).
!!! tip
This is the main line that you would have to modify if you wanted to use a different database.
Create the SQLAlchemy engine
{!./src/sql_databases/tutorial001.py!}
Note
The argument:
connect_args={"check_same_thread": False}
...is needed only for SQLite. It's not needed for other databases.
!!! info "Technical Details"
That argument `check_same_thread` is there mainly to be able to run the tests that cover this example.
Create a Session class
Each instance of the Session class will have a connection to the database.
This is not a connection to the database yet, but once we create an instance of this class, that instance will have the actual connection to the database.
{!./src/sql_databases/tutorial001.py!}
Create a middleware to handle sessions
Now let's temporarily jump to the end of the file, to use the Session class we created above.
We need to have an independent Session per request, use the same session through all the request and then close it after the request is finished.
And then a new session will be created for the next request.
For that, we will create a new middleware.
A "middleware" is a function that is always executed for each request, and have code before and after the request.
The middleware we will create (just a function) will create a new SQLAlchemy Session for each request, add it to the request and then close it once the request is finished.
{!./src/sql_databases/tutorial001.py!}
About request.state
request.state is a property of each Starlette Request object, it is there to store arbitrary objects attached to the request itself, like the database session in this case.
For us in this case, it helps us ensuring a single session/database-connection is used through all the request, and then closed afterwards (in the middleware).
Create a CustomBase model
This is more of a trick to facilitate your life than something required.
But by creating this CustomBase class and inheriting from it, your models will have automatic __tablename__ attributes (that are required by SQLAlchemy).
That way you don't have to declare them explicitly in every model.
So, your models will behave very similarly to, for example, Flask-SQLAlchemy.
{!./src/sql_databases/tutorial001.py!}
Create the SQLAlchemy Base model
{!./src/sql_databases/tutorial001.py!}
Create your application data model
Now this is finally code specific to your app.
Here's a user model that will be a table in the database:
{!./src/sql_databases/tutorial001.py!}
Initialize your application
In a very simplistic way, initialize your database (create the tables, etc) and make sure you have a first user:
{!./src/sql_databases/tutorial001.py!}
!!! info
Notice that we close the session with db_session.close().
We close this session because we only used it to create this first user.
Every new request will get its own new session.
Note
Normally you would probably initialize your database (create tables, etc) with Alembic.
And you would also use Alembic for migrations (that's its main job). For whenever you change the structure of your database, add a new column, a new table, etc.
The same way, you would probably make sure there's a first user in an external script that runs before your application, or as part of the application startup.
In this example we are doing those two operations in a very simple way, directly in the code, to focus on the main points.
Also, as all the functionality is self-contained in the same code, you can copy it and run it directly, and it will work as is.
Get a user
By creating a function that is only dedicated to getting your user from a user_id (or any other parameter) independent of your path operation function, you can more easily re-use it in multiple parts and also add unit tests for it:
{!./src/sql_databases/tutorial001.py!}
Create your FastAPI code
Now, finally, here's the standard FastAPI code.
Create your app and path operation function:
{!./src/sql_databases/tutorial001.py!}
We are creating the database session before each request, attaching it to the request, and then closing it afterwards.
All of this is done in the middleware explained above.
Because of that, we can use the Request to access the database session with request._scope["db"].
Then we can just call get_user directly from inside of the path operation function and use that session.
Create the path operation function
Here we are using SQLAlchemy code inside of the path operation function, and in turn it will go and communicate with an external database.
That could potentially require some "waiting".
But as SQLAlchemy doesn't have compatibility for using await directly, as would be with something like:
user = await get_user(db_session, user_id=user_id)
...and instead we are using:
user = get_user(db_session, user_id=user_id)
Then we should declare the path operation without async def, just with a normal def:
{!./src/sql_databases/tutorial001.py!}
Migrations
Because we are using SQLAlchemy directly and we don't require any kind of plug-in for it to work with FastAPI, we could integrate database migrations with Alembic directly.
You would probably want to declare your database and models in a different file or set of files, this would allow Alembic to import it and use it without even needing to have FastAPI installed for the migrations.
Check it
You can copy this code and use it as is.
!!! info
In fact, the code shown here is part of the tests. As most of the code in these docs.
You can copy it, let's say, to a file main.py.
Then you can run it with Uvicorn:
uvicorn main:app --debug
And then, you can open your browser at http://127.0.0.1:8000/docs.
And you will be able to interact with your FastAPI application, reading data from a real database:
Response schema and security
This section has the minimum code to show how it works and how you can integrate SQLAlchemy with FastAPI.
But it is recommended that you also create a response model with Pydantic, as described in the section about Extra Models.
That way you will document the schema of the responses of your API, and you will be able to limit/filter the returned data.
Limiting the returned data is important for security, as for example, you shouldn't be returning the hashed_password to the clients.
That's something that you can improve in this example application, here's the current response data:
{
"is_active": true,
"hashed_password": "notreallyhashed",
"email": "[email protected]",
"id": 1
}
Interact with the database direclty
If you want to explore the SQLite database (file) directly, independently of FastAPI, to debug its contents, add tables, columns, records, modify data, etc. you can use DB Browser for SQLite.
It will look like this:
