pydantic_field_validator_decorator_for_custom_validation.py

1from pydantic import BaseModel, field_validator
2
3
4class UserModel(BaseModel):
5    name: str
6    username: str
7
8    @field_validator('username')
9    @classmethod
10    def username_alphanumeric(cls, v: str) -> str:
11        assert v.isalnum(), 'must be alphanumeric'
12        return v
13
14
15print(UserModel(name='John Doe', username='johndoe123'))
16#> name='John Doe' username='johndoe123'