List Parameters

Learn the fundamentals of list parameters in FastAPI.

🎯 Core Concept

List query parameters allow passing multiple values for the same parameter. They're useful for filtering by multiple criteria like tags, categories, or IDs.

📖 What You'll Learn

In this section, you'll understand:

• Multiple values for single parameter

• Using Query() for list parameters

• Common list patterns

• Real-world filtering scenarios

💡 List Query Parameters Example

from fastapi import FastAPI, Query

app = FastAPI()

@app.get("/items")
async def list_items(tags: list[str] = Query(default=[])):
    # GET /items?tags=python&tags=fastapi
    return {"tags": tags}

@app.get("/products")
async def search_products(
    categories: list[str] = Query(default=[]),
    ids: list[int] = Query(default=[])
):
    # GET /products?categories=electronics&categories=books&ids=1&ids=2
    return {"categories": categories, "ids": ids}

Real-World Usage

List parameters are essential for:

• **Tag filtering**: Multiple tags to filter

• **Category selection**: Multiple categories

• **ID lookups**: Get multiple items by ID

• **Permission scopes**: Multiple access levels

🔑 Key Takeaways

• ✅ Understand the purpose of list parameters

• ✅ Know when to apply this pattern

• ✅ Recognize its benefits in real-world scenarios

• ✅ Be prepared to use it in your projects

Ready to explore more? Check out the advanced section for production patterns and edge cases.