Dependency Injection

Dependency Injection (DI) is a powerful pattern in Ignyx that allows you to declare dependencies for your route handlers. Ignyx then takes care of resolving these dependencies, providing you with the necessary objects automatically.

Overview

The Depends() pattern allows you to write reusable logic that can be shared across multiple routes. This is useful for: - Authentication and authorization - Database connection management - Shared configuration - Request pre-processing

When you use Depends(), Ignyx calls the dependency for you and passes the result to your handler.

Basic Example

Here's a simple example of using Depends() to extract a token from a header.

from ignyx import Ignyx, Depends, Request

app = Ignyx()

def get_current_user(request: Request):
    token = request.headers.get("Authorization")
    if not token:
        # In a real app, you would raise an HTTPException here
        return "Anonymous"
    return {"id": 1, "name": "Saketh"}

@app.get("/users/me")
def read_current_user(user = Depends(get_current_user)):
    return user

Advanced Example: Chained Dependencies

Dependencies can also depend on other dependencies, allowing you to create complex authentication or data retrieval chains.

from ignyx import Ignyx, Depends, Request

app = Ignyx()

def get_db():
    return {"session": "active_db_session"}

def get_current_user(db = Depends(get_db)):
    # Use db session to find user
    return {"id": 1, "username": "sakethdevx"}

def get_active_user(user = Depends(get_current_user)):
    if user.get("disabled"):
        raise HTTPException(400, "User inactive")
    return user

@app.get("/items")
def read_items(user = Depends(get_active_user)):
    return {"user": user, "items": ["item1", "item2"]}

Generator Dependencies

Ignyx supports generator dependencies using yield. This is perfect for resources that need cleanup, such as database sessions or file handles.

def get_db():
    db = DatabaseSession()
    try:
        yield db
    finally:
        db.close() # cleanup happens after route execution

Testing

You can easily override dependencies in your tests using the dependency_overrides attribute of the Ignyx app or TestClient.

from ignyx.testclient import TestClient

def override_get_current_user():
    return {"id": 999, "name": "Test User"}

app.dependency_overrides[get_current_user] = override_get_current_user

client = TestClient(app)
response = client.get("/users/me")
assert response.json()["id"] == 999

API Reference

Depends(dependency, use_cache=True)

• dependency: A callable (function, class).
• use_cache: If True, the result of the dependency is cached for the duration of a single request. If multiple routes or dependencies depend on the same callable, it will only be executed once per request.