fastapi-async-patterns

FastAPI Async Patterns Skill

When to Use

Use this skill when:

• Creating new FastAPI endpoints with async support
• Building service layers with dependency injection
• Implementing repository patterns for data access
• Adding pagination, filtering, or search
• Integrating with async databases (SQLAlchemy async)
• Handling Gemini AI integration with fallbacks
• Creating proper error handling and validation

Key Patterns

1. Service Layer Architecture

# services/product_service.py
from typing import Optional, List
from sqlalchemy.ext.asyncio import AsyncSession
from app.models import Product
from app.repositories import ProductRepository
from app.schemas import ProductCreate, ProductResponse

class ProductService:
    def __init__(self, db: AsyncSession):
        self.repository = ProductRepository(db)
    
    async def create_product(self, product_data: ProductCreate) -> ProductResponse:
        """Create product with validation and error handling"""
        existing = await self.repository.get_by_slug(product_data.slug)
        if existing:
            raise ValueError(f"Product slug '{product_data.slug}' already exists")
        
        product = await self.repository.create(product_data.dict())
        return ProductResponse.from_orm(product)
    
    async def list_products(
        self,
        skip: int = 0,
        limit: int = 10,
        category: Optional[str] = None
    ) -> List[ProductResponse]:
        """List products with pagination and filtering"""
        filters = {}
        if category:
            filters['category'] = category
        
        products = await self.repository.list(skip=skip, limit=limit, filters=filters)
        return [ProductResponse.from_orm(p) for p in products]
    
    async def search_products(self, query: str) -> List[ProductResponse]:
        """Full-text search with Gemini enrichment"""
        products = await self.repository.search(query)
        # Optional: Enhance with Gemini insights
        return [ProductResponse.from_orm(p) for p in products]