Junior — Middle

What is the role of dependency injection in FastAPI and why is it necessary?

sobes.tech AI

Answer from AI

Dependency Injection (DI) in FastAPI is used to manage dependencies between application components, such as connecting to a database, obtaining the current user, configuring caching, etc. This allows:

To eliminate tight coupling of components.
To improve testability of the code, as dependencies can be easily replaced.
To centrally manage the creation and lifecycle of objects.

FastAPI implements DI through parameterization of handler functions using Depends. For example:

from fastapi import FastAPI, Depends

def get_db():
    db = create_db_session()
    try:
        yield db
    finally:
        db.close()

app = FastAPI()

@app.get("/items/")
def read_items(db=Depends(get_db)):
    items = db.query(Item).all()
    return items

Here, get_db is a dependency that is automatically injected into the handler. This simplifies resource management and enhances the modularity of the application.

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