How to allow only ISO8601 timestamp in query parameter

[ahmedrafayat]

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Example Code

from datetime import datetime
from fastapi import FastAPI, Query


app = FastAPI()

@app.get("/test")
def test_route(time_1: datetime = Query()):
    print(time_1)  # This is always a datetime
    return time_1

Description

Case 1:

• Open browser and request to /test?time_1=123
• datetime is logged in the console "1970-01-01T00:02:03+00:00"
• Returned response is "1970-01-01T00:02:03+00:00"

Case 2:

• Open browser and request to /test?time_1=2023-07-20T21:33:33.232Z
• datetime is logged in the console "2023-07-20T21:33:33.232000+00:00"
• Returned response is "2023-07-20T21:33:33.232000+00:00"

This is fine, and expected. But I need to not allow case 2, and throw error if case 1. Meaning if time_1 is not a valid ISOFormat, I want to throw error. These are the solutions I tried.

Solution I tried:

from datetime import datetime
from fastapi import Depends, FastAPI, Query
from pydantic import BaseModel, validator


app = FastAPI()



class QueryParams(BaseModel):
    time_1: str = Query()
    
    @validator('time_1')
    def validator_datetime(cls, value):
        try:
            return datetime.strptime(value, "%Y-%m-%dT%H:%M%z")  # special date format without seconds and microseconds
        except ValueError as error:
            raise ValueError("Invalid datetime") from error

@app.get("/test")
def test_route(time_1: QueryParams = Depends()):
    print(time_1)
    return time_1

This validates the query param, but raising ValueError here returns "Internal Server Error". So needed to add an exception handler, and so the updated code:

from datetime import datetime
from fastapi import Depends, FastAPI, Query
from fastapi.encoders import jsonable_encoder
from fastapi.responses import JSONResponse
from pydantic import BaseModel, validator


app = FastAPI()

@app.exception_handler(ValueError)
def handle_value_error(request, exc):
    return JSONResponse(
        status_code=422,
        content={"detail": jsonable_encoder(exc.errors()), "status": 422},
    )

class QueryParams(BaseModel):
    time_1: str = Query()
    
    @validator('time_1')
    def validator_datetime(cls, value):
        try:
            return datetime.strptime(value, "%Y-%m-%dT%H:%M%z")  # special date format without seconds and microseconds
        except ValueError as error:
            raise ValueError("Invalid datetime") from error

@app.get("/test")
def test_route(time_1: QueryParams = Depends()):
    print(time_1)
    return time_1

Problem with Solution:

1. The returned Json response for Case 1 now is

{
  "detail": [
    {
      "loc": [
        "time_1"
      ],
      "msg": "Invalid datetime",
      "type": "value_error"
    }
  ],
  "status": 422
}

but expected

{
  "detail": [
    {
      "loc": [
       "query",   // This is missing
        "time_1"
      ],
      "msg": "Invalid datetime",
      "type": "value_error"
    }
  ],
  "status": 422
}

Operating System

Linux, macOS

Operating System Details

Enviroments:

1. Macos
2. Docker container running in Docker desktop in MacOS

FastAPI Version

0.81.0

Python Version

3.9.16

Additional Context

No response

[jgould22]

What happens if you return a pydantic.ValidationError in validator_datetime?

[ahmedrafayat]

pydantic.ValidationError expects 3 arguments. I would have to manually build them. Can you suggest how I can do that?

[YuriiMotov]

You can implement this using PlainValidator:

from datetime import datetime
from typing import Annotated, TypeAlias
from fastapi import FastAPI, Query
from pydantic import PlainValidator

app = FastAPI()

def validate_date_time(value: str):
    try:
        return datetime.strptime(value, "%Y-%m-%dT%H:%M%z")
    except ValueError as error:
        raise ValueError("Invalid datetime") from error

MyDateTime: TypeAlias = Annotated[datetime, PlainValidator(validate_date_time)]

@app.get("/test")
def test_route(time_1: Annotated[MyDateTime, Query(description="ISO8601 timestamp")]):
    print(time_1)  # This is always a datetime
    return time_1