Multiple Bodies

Learn the fundamentals of multiple bodies in FastAPI.

🎯 Core Concept

You can combine multiple request body models in a single endpoint using type unions or embedding objects. This allows accepting complex request structures with multiple related data models.

📖 What You'll Learn

In this section, you'll understand:

• Combining multiple body parameters

• Using Body() to specify embeddings

• Union types for flexible requests

• Real-world multi-model endpoints

• Complex request structures

💡 Multiple Body Models Example

from fastapi import FastAPI, Body
from pydantic import BaseModel

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float

class Order(BaseModel):
    order_id: str
    items: list[Item]

@app.post("/process/")
async def process(
    order: Order = Body(...),
    priority: int = Body(..., embed=True)
):
    return {"order": order, "priority": priority}

🔍 Body Embedding

# Use Body() with embed=True to wrap single values
@app.post("/items/")
async def create_item(
    item: Item,
    quantity: int = Body(..., embed=True)
):
    # Request: {"item": {...}, "quantity": 5}
    return {"item": item, "quantity": quantity}

Real-World Usage

Multiple bodies are used for:

• **Complex operations**: Multiple related objects

• **Metadata + data**: Both data and processing params

• **Transactions**: Order items + billing address

🔑 Key Takeaways

• ✅ Understand the purpose of multiple bodies

• ✅ 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.