Why do I get "Validators defined with incorrect fields" when trying to validate JSON data using pydantic?

Question

I am trying to parse a JSON object to pydantic validator and it's giving a compiler error.

pydantic.errors.ConfigError: Validators defined with incorrect fields: validate_grade

{
  "grade": "A"
  "subject": [
    {
      "physics": "PHY",
      "chemistry": "CHE",
      "classTime": {
    "date": "2024-03-25",
    "time": null
      },
      "labTime":null
      }
    }
  ]
}

The implementation code:

class Grade(BaseModel):
    @validator("grade")
    def validate_grade(cls, val):
        if (val == None):
            raise ValueError("grade is null")     

class subject(BaseModel): 
    @validator("classTime", pre=True, always=True)
    def validate_classTime(cls, value, values):
        date_str = value.get('date', '')
        time_str = value.get('time', '')

The above implementation is throwing the error after adding the section:

class Grade(BaseModel):     

I also want to get the "grade" inside the class subject. I tried different options after referring to the similar implementations, but there is no luck.

Answer 1

There is no model that contains grade and subject fields.

from pydantic import BaseModel, validator
from typing import List, Optional
from datetime import date, time


class ClassTime(BaseModel):
    date: Optional[date]
    time: Optional[time]


class Subject(BaseModel):
    physics: str
    chemistry: str
    classTime: Optional[ClassTime]
    labTime: Optional[str]


class Student(BaseModel):
    grade: str
    subject: List[Subject]

    @validator("grade")
    def validate_grade(cls, val):
        if val is None:
            raise ValueError("grade is null")
        return val

    @validator("subject", each_item=True)
    def validate_subject(cls, val):
        if val.classTime:
            if not val.classTime.date:
                raise ValueError("classTime.date is null")
        return val


json_data = {
    "grade": "A",
    "subject": [
        {
            "physics": "PHY",
            "chemistry": "CHE",
            "classTime": {
                "date": "2024-03-25",
                "time": None
            },
            "labTime": None
        }
    ]
}

student = Student(**json_data)
print(student)

Output:

grade='A' subject=[Subject(physics='PHY', chemistry='CHE', classTime=ClassTime(date=datetime.date(2024, 3, 25), time=None), labTime=None)]