FastAPI - Postman error 422 Unprocessable Entity

Question

I am using FastAPI to make get/post/put/del requests, which all work perfectly fine in the browser. I wanted to use Postman to do the exact same thing; however, I am running into an issue trying to do anything other than get. Below is the error I am getting:

{
    "detail": [
        {
            "loc": [
                "body"
            ],
            "msg": "field required",
            "type": "value_error.missing"
        }
    ]
}

422 Unprocessable Entity is the exact error.

Below is the code I am using:

from lib2to3.pytree import Base
from fastapi import FastAPI, Path, Query, HTTPException, status, File, Form
from typing import Optional, Dict, Type
from pydantic import BaseModel
import inspect

app = FastAPI()

class Item(BaseModel):
    name: str
    price: float
    brand: Optional[str] = None


class UpdateItem(BaseModel):
    name: Optional[str] = None
    price: Optional[float] = None
    brand: Optional[str] = None


inventory = {}

@app.get("/get-item/{item_id}")
def get_item(item_id: int = Path(None, description = "The ID of the item")):
    if item_id not in inventory:
        raise HTTPException(status_code = 404, detail = "Item ID not found")
    return inventory[item_id]
    

@app.get("/get-by-name/")
def get_item(name: str = Query(None, title = "Name", description = "Test")):
    for item_id in inventory:
        if inventory[item_id].name == name:
            return inventory[item_id]
    # return {"Data": "Not found"}
    raise HTTPException(status_code = 404, detail = "Item ID not found")


@app.post("/create-item/{item_id}")
def create_item(item_id: int, item: Item):
    if item_id in inventory:
        raise HTTPException(status_code = 400, detail = "Item ID already exists")

    inventory[item_id] = item
    print(type(item))
    return inventory[item_id]
    

@app.put("/update-item/{item_id}")
def update_item(item_id: int, item: UpdateItem):
    if item_id not in inventory:
        # return {"Error": "Item does not exist"}
        raise HTTPException(status_code = 404, detail = "Item ID not found")

    if item.name != None:
        inventory[item_id].name = item.name
    if item.brand != None:
        inventory[item_id].brand = item.brand
    if item.price != None:
        inventory[item_id].price = item.price
    
    return inventory[item_id]


@app.delete("/delete-item/{item_id}")
def delete_item(item_id: int = Query(..., description="ID of item you want to delete", ge=0)):
    if item_id not in inventory:
        # return {"Error": "ID does not exist"}
        raise HTTPException(status_code = 404, detail = "Item ID not found")
    del inventory[item_id]
    return {"Success": "Item deleted"}

I tried this possible solution with no luck: https://github.com/tiangolo/fastapi/issues/2387

Answer 1

Your endpoint expects Item as JSON (body) data, but the screenshot you provided shows that you are sending the required fields as Query parameters (using the Params tab in Postman); hence, the error that the body is missing. You should instead add your data to the body of your POST request in Postman. To do that, you should go to Body > raw, and select JSON from the dropdown list to indicate the format of your data. Your payload should look something like this:

{
 "name": "foo",
 "price": 1.50
}

If you needed to pass the Item model parameters as Query parameters, you should then use Depends(), as described in this answer (Method 2).