Fastapi Router Py

---
name: fastapi-router-py
description: Create FastAPI routers with CRUD operations, authentication dependencies, and proper response models. Use when building REST API endpoints, creating new routes, implementing CRUD operations, or adding authenticated endpoints in FastAPI applications.
license: MIT
metadata:
  author: Microsoft
  version: "1.0.0"
---

# FastAPI Router

Create FastAPI routers following established patterns with proper authentication, response models, and HTTP status codes.

## Quick Start

Copy the template from [assets/template.py](assets/template.py) and replace placeholders:
- `{{ResourceName}}` → PascalCase name (e.g., `Project`)
- `{{resource_name}}` → snake_case name (e.g., `project`)
- `{{resource_plural}}` → plural form (e.g., `projects`)

## Authentication Patterns

```python
# Optional auth - returns None if not authenticated
current_user: Optional[User] = Depends(get_current_user)

# Required auth - raises 401 if not authenticated
current_user: User = Depends(get_current_user_required)
```

## Response Models

```python
@router.get("/items/{item_id}", response_model=Item)
async def get_item(item_id: str) -> Item:
    ...

@router.get("/items", response_model=list[Item])
async def list_items() -> list[Item]:
    ...
```

## HTTP Status Codes

```python
@router.post("/items", status_code=status.HTTP_201_CREATED)
async def create_item(item: ItemCreate) -> Item:
  ...

@router.delete("/items/{id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_item(id: str) -> None:
  ...
```

## Integration Steps

1. Create router in `src/backend/app/routers/`
2. Mount in `src/backend/app/main.py`
3. Create corresponding Pydantic models
4. Create service layer if needed
5. Add frontend API functions

## Best Practices

1. **Pick `def` or `async def` per endpoint based on whether you call async I/O; do not call blocking I/O from an `async def` handler.**
2. **Manage long-lived resources (DB pools, HTTP clients) in `lifespan` and inject via `Depends`;** use `with`/`async with` for per-request resources.

## Reference Files

| File | Contents |
|------|----------|
| [references/capabilities.md](references/capabilities.md) | Additional non-hero capabilities, operation-group coverage, and production checklists. |