fastapi-api-patterns

# fastapi-api-patterns

## Instructions

This skill provides comprehensive REST API design patterns and implementation templates for FastAPI applications. It covers CRUD operations, pagination, filtering, request/response models, error handling, and API organization following modern best practices.

### 1. CRUD Endpoint Patterns

Create, Read, Update, Delete endpoints using FastAPI routers:

```bash
# Use CRUD template to generate complete endpoint set
cp ./skills/fastapi-api-patterns/templates/crud_endpoint.py app/routers/items.py

# Customize for your model
# - Replace Item model with your Pydantic model
# - Update database operations
# - Add authentication dependencies
```

**What This Provides:**
- `POST /items/` - Create new item
- `GET /items/{item_id}` - Read single item by ID
- `GET /items/` - Read multiple items with pagination
- `PUT /items/{item_id}` - Update entire item
- `PATCH /items/{item_id}` - Partial update
- `DELETE /items/{item_id}` - Delete item

**Router Structure:**
```python
from fastapi import APIRouter, HTTPException, Depends, status
from typing import List

router = APIRouter(
    prefix="/items",
    tags=["items"],
    responses={404: {"description": "Not found"}},
)
```

### 2. Pagination and Filtering

Implement pagination with query parameters:

```bash
# Use pagination template
cp ./skills/fastapi-api-patterns/templates/pagination.py app/utils/pagination.py
```

**Pagination Strategies:**

**1. Offset-Based Pagination (Simple):**
```python
@router.get("/items/")
async def list_items(skip: int = 0, limit: int = 10):
    return items[skip : skip + limit]
```

**2. Cursor-Based Pagination (Performance):**
```python
@router.get("/items/")
async def list_items(cursor: str | None = None, limit: int = 10):
    # Use last item ID as cursor for next page
    # Better for large datasets
```

**3. Page-Based Pagination (User-Friendly):**
```python
@router.get("/items/")
async def list_items(page: int = 1, page_size: int = 10):
    skip = (page