title: Body — Updates
description: Implement partial updates (PATCH) with Pydantic models in JustAPI.
keywords: [JustAPI, PATCH, partial update, body updates, Pydantic]

PUT vs PATCH

• PUT — full replacement. The client sends the entire resource.
• PATCH — partial update. The client sends only the fields to change.

Full Update with PUT

from pydantic import BaseModel
from justapi import JustAPIApp

class Item(BaseModel):
    name: str
    price: float
    description: str = ""

app = JustAPIApp()

@app.put("/items/{item_id}")
def update_item(item_id: int, item: Item):
    return {"item_id": item_id, **item.model_dump()}

Partial Update with PATCH

Use exclude_unset=True to get only the fields the client explicitly sent:

@app.patch("/items/{item_id}")
def partial_update(item_id: int, item: Item):
    update_data = item.model_dump(exclude_unset=True)
    # update_data only contains fields the client sent
    return {"item_id": item_id, "updates": update_data}

If the client sends {"name": "New Name"}, only name is in update_data.

Optional Model

from typing import Optional

class ItemUpdate(BaseModel):
    name: Optional[str] = None
    price: Optional[float] = None
    description: Optional[str] = None

@app.patch("/items/{item_id}")
def partial_update(item_id: int, item: ItemUpdate):
    update_data = item.model_dump(exclude_unset=True)
    return {"item_id": item_id, "updates": update_data}

See Also

• Request Body — full request body usage
• Body — Multiple Parameters — mixing parameter sources