How to Set Up And Tear Down A Database Between Tests In Fastapi?

Published on Sep 20, 2025

7 min read

How to handle database schema migrations in FastAPI?
How to populate a test database with sample data in FastAPI?
How to handle database errors in FastAPI?
How to perform CRUD operations on a test database in FastAPI?
How to run database migrations in FastAPI?

How to Set Up And Tear Down A Database Between Tests In Fastapi? image

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In FastAPI, you can set up and tear down a database between tests by leveraging fixtures in a testing framework like pytest.

To set up a database connection for testing, you can create a fixture function that establishes a connection to the database and returns it to the test functions that need it. This fixture function can be scoped to the module or to a specific test session, depending on your testing requirements.

You can then use this fixture function in your test functions by including it as an argument and using it to interact with the database during testing.

After each test has been executed, you can tear down the database connection by closing it in a fixture function marked with the @pytest.fixture(autouse=True) decorator. This ensures that the database connection is cleaned up properly between tests, preventing any potential issues with state persistence or resource leaks.

By setting up and tearing down the database between tests using fixtures, you can ensure that each test is run in isolation and has a clean database environment to work with, improving the reliability and consistency of your test suite in FastAPI.

How to handle database schema migrations in FastAPI?

FastAPI does not provide built-in support for database schema migrations, but you can use a separate library like Alembic or Flask-Migrate to handle database schema migrations in FastAPI. Here's a general guide on how to handle database schema migrations in FastAPI:

Install a database migration library: First, install a database migration library like Alembic or Flask-Migrate using pip.
Create a migration repository: After installing the migration library, create a migration repository by running the migration initialization command provided by the library.
Define database models: Define your database models using SQLAlchemy ORM or any other ORM of your choice.
Generate a migration: Whenever you make changes to your database schema, generate a new migration by running the migration generation command provided by the migration library.
Apply migrations: Apply the generated migrations to your database by running the migration application command provided by the migration library.
Update your FastAPI application: Update your FastAPI application to reflect the changes in the database schema.

By following these steps, you can handle database schema migrations in FastAPI using a separate migration library like Alembic or Flask-Migrate.

How to populate a test database with sample data in FastAPI?

To populate a test database with sample data in FastAPI, you can create a script that uses SQLAlchemy or any other ORM library to interact with your database.

Here's an example script that uses SQLAlchemy to populate a database with sample data in FastAPI:

Install SQLAlchemy and any required database drivers:

pip install fastapi[all] sqlalchemy

Create a new file named populate_db.py and import the necessary modules:

from sqlalchemy import create_engine from sqlalchemy.orm import sessionmaker from models import Base, User # Import your models

Create a function to populate the database with sample data:

def populate_db(): engine = create_engine('sqlite:///test.db') # Change the database URL based on your setup Session = sessionmaker(bind=engine) session = Session()

# Create sample users
users = \[
    User(name='Alice', email='alice@example.com'),
    User(name='Bob', email='bob@example.com'),
    User(name='Charlie', email='charlie@example.com')
\]

# Add users to the session and commit changes
session.add\_all(users)
session.commit()

Run the script to populate the database with sample data:

if __name__ == '__main__': populate_db() print('Sample data added to the database.')

Create a models.py file to define your database models:

from sqlalchemy import Column, Integer, String from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base): __tablename__ = 'users'

id = Column(Integer, primary\_key=True, index=True)
name = Column(String)
email = Column(String)

Run the populate_db.py script to add sample data to the database:

python populate_db.py

After running the script, your test database should be populated with sample data. You can now use FastAPI to interact with the database and test your API endpoints.

How to handle database errors in FastAPI?

In FastAPI, you can handle database errors by using exception handlers. When an error occurs during a database operation, FastAPI will raise an exception that you can catch and handle appropriately.

Here is an example of how you can handle database errors in FastAPI:

Define a new exception class to handle database errors:

class DatabaseError(Exception): def __init__(self, message): self.message = message

Create an exception handler to catch database errors and return an appropriate response:

from fastapi import FastAPI, HTTPException from starlette.requests import Request from starlette.responses import JSONResponse

app = FastAPI()

@app.exception_handler(DatabaseError) async def database_error_handler(request: Request, exc: DatabaseError): return JSONResponse( status_code=500, content={"message": "Database error: " + exc.message} )

Raise the DatabaseError exception wherever you encounter a database error in your application code:

@app.get("/") async def read_item(): try: # Perform database operation here except DatabaseError as e: raise DatabaseError("Failed to retrieve data from database")

By following these steps, you can effectively handle database errors in FastAPI and provide a consistent and informative response to users when errors occur.

How to perform CRUD operations on a test database in FastAPI?

To perform CRUD operations on a test database in FastAPI, you can follow these steps:

Set up the database connection: You can use libraries like SQLAlchemy or Tortoise ORM to connect to your database from your FastAPI application.
Create a model: Define a model for your database table that contains the fields you want to store in the database. For example, you can create a Pydantic model like this:

from pydantic import BaseModel

class Item(BaseModel): name: str description: str

Create routes for CRUD operations: Create routes in your FastAPI app that handle the operations to create, read, update, and delete data in your database.

from fastapi import FastAPI from typing import List from .models import Item

app = FastAPI()

items = []

@app.post("/items/") async def create_item(item: Item): items.append(item) return item

@app.get("/items/", response_model=List[Item]) async def read_items(): return items

@app.get("/items/{item_id}", response_model=Item) async def read_item(item_id: int): return items[item_id]

@app.put("/items/{item_id}") async def update_item(item_id: int, item: Item): items[item_id] = item return item

@app.delete("/items/{item_id}") async def delete_item(item_id: int): del items[item_id] return {"message": "Item deleted successfully"}

Test the CRUD operations: You can use tools like Postman or curl to test the CRUD operations by sending requests to the routes you defined in your FastAPI app.

By following these steps, you can perform CRUD operations on a test database in FastAPI.

How to run database migrations in FastAPI?

To run database migrations in FastAPI, you will need to use a database migration tool such as Alembic. Alembic is a lightweight database migration tool for SQLAlchemy that allows you to create and manage database migrations with ease.

Here are the steps to run database migrations in FastAPI using Alembic:

Install Alembic by running the following command in your terminal:

pip install alembic

Set up your database connection using SQLAlchemy. You can configure your database connection in the SQLALCHEMY_DATABASE_URL environment variable.
Initialize Alembic in your project by running the following command in your terminal:

alembic init alembic

This will create an alembic directory in your project that contains the necessary configuration files for Alembic.

Create a new migration script using Alembic by running the following command in your terminal:

alembic revision --autogenerate -m "Add table"

This will generate a new migration script in the alembic/versions directory that contains the necessary changes to your database schema.

Apply the migration to your database by running the following command in your terminal:

alembic upgrade head

This will apply the migration script to your database and update the schema accordingly.

By following these steps, you can run database migrations in FastAPI using Alembic. It's important to note that you can customize the migration scripts generated by Alembic to include additional database schema changes as needed for your project.