with Pydantic, how can i create my own ValidationError reason

Question

it seems impossible to set a regex constraint with a __root__ field like this one:

class Cars(BaseModel):
    __root__: Dict[str, CarData]

so, i’ve resorted to doing it at the endpoint:

@app.post("/cars")
async def get_cars(cars: Cars = Body(...)):
    x = cars.json()
    y = json.loads(x)
    keys = list(y.keys())
    try:
        if any([re.search(r'^d+$', i) is None for i in keys]):
            raise ValidationError
    except ValidationError as ex:
        return 'wrong type'
    return 'works'

this works well in that i get wrong type returned if i dont use a digit in the request body.

but i’d like to return something similar to what pydantic returns but with a custom message:

{
  "detail": [
    {
      "loc": [
        "body",
        "__root__",
      ],
      "msg": "hey there, you can only use digits!",
      "type": "type_error.???"
    }
  ]
}

Asked By: avnav99

||

Source

Answer 1

You can pass your own error string by using raise ValidationError("Wrong data type").
Hope it helps.

Answered By: Shashi Kant

Answer 2

if it helps anyone, here is how i validated a dynamic field:

class Cars(BaseModel):
    __root__: Dict[str, CarData]
    
    @pydantic.root_validator(pre=True)
    @classmethod
    def car_id_is_digit(cls, fields):
        car_ids = list(list(fields.values())[0].keys())
        print(car_ids)
        if any([bool(re.search(r'^d+$', car_id)) == False for car_id in car_ids]):
            raise ValueError("car_id must be a string that is a digit.")
        else:
            return fields

since a regular field validator requires a field name as an argument, i used the root_validator which validates all fields – and does not require that argument.

all this, because __root__ cannot be referenced in the regular field validator, it seems.

however, this means you can only have __root__ fields – and they will all be under the same validation rules…not sure how to added more fields with this.

Answered By: avnav99

with Pydantic, how can i create my own ValidationError reason

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