Dataclass to Pydantic BaseModel

dataclass_to_pydantic.py

import unittest
from typing import Any, Type
from dataclasses import dataclass, is_dataclass

from pydantic import BaseModel, ValidationError
from pydantic.main import MetaModel


AnyType = Type[Any]

def from_dataclass(DataClass: AnyType) -> BaseModel:

    def _get_model(DataClass: AnyType) -> BaseModel:
        for field_name, field_type in DataClass.__annotations__.items():
            if is_dataclass(field_type):
                field = _get_model(field_type)
                DataClass.__annotations__[field_name] = field

        namespace = {
            '__annotations__': DataClass.__annotations__,
            '__module__': DataClass.__module__,
            '__qualname__': DataClass.__qualname__
        }
        return MetaModel(DataClass.__name__, (BaseModel,), namespace)

    return _get_model(DataClass)


class ModelTest(unittest.TestCase):


    def test_simple_success(self):
        @dataclass
        class SimpleDataClass:
            val: int

        SimpleModel = from_dataclass(SimpleDataClass)
        data = {'val': 123}
        res = SimpleModel(**data)
        self.assertEqual(res.dict(), data)

    def test_simple_validation_error(self):
        @dataclass
        class SimpleDataClass:
            val: int

        SimpleModel = from_dataclass(SimpleDataClass)
        data = {'val': 'word'}
        with self.assertRaises(ValidationError):
            SimpleModel(**data)

    def test_nested_success(self):
        @dataclass
        class DataClassInner:
            inner_val: str

        @dataclass
        class NestedDataClass:
            val: str
            inner_data_class: DataClassInner

        NestedModel = from_dataclass(NestedDataClass)
        data = {'val': 'word', 'inner_data_class': {'inner_val': 'word'}}
        res = NestedModel(**data)
        self.assertEqual(res.dict(), data)

    def test_nested_validation_error(self):
        @dataclass
        class DataClassInner:
            inner_val: int

        @dataclass
        class NestedDataClass:
            val: str
            inner_data_class: DataClassInner

        NestedModel = from_dataclass(NestedDataClass)
        data = {'val': 'word', 'inner_data_class': {'inner_val': 'word'}}
        with self.assertRaises(ValidationError):
            NestedModel(**data)


if __name__ == '__main__':
    unittest.main(verbosity=2)