CommaSeparatedList[T]

comma_separated_list.py

from typing import Generic, TypeVar

from pydantic import ValidationError
from pydantic.fields import ModelField

T = TypeVar('T')


class CommaSeparatedList(Generic[T]):
    """Parse and validate a list of comma separated values."""
    def __init__(self, value: T):
        self.value = value

    @classmethod
    def __get_validators__(cls):
        yield cls.validate

    @classmethod
    def validate(cls, v, field: ModelField):
        if not isinstance(v, str):
            raise TypeError('Expected a string.')

        if not field.sub_fields:
            # Generic parameters were not provided so we don't try to validate
            # them and just return the value as is
            return v

        value_type = field.sub_fields[0]
        sub_values = v.split(',')

        pairs = [
            value_type.validate(
                sub_value,
                {},
                loc=str(i),
            ) for i, sub_value in enumerate(sub_values)
        ]

        valid_values, errors = zip(*pairs)

        errors = list(filter(bool, errors))
        if errors:
            raise ValidationError(errors, cls)

        return list(valid_values)

test_comma_separated_list.py

from pydantic import BaseModel, ValidationError

from crudantic.types import CommaSeparatedList


class StrListModel(BaseModel):
    lst: CommaSeparatedList[str]


class IntListModel(BaseModel):
    lst: CommaSeparatedList[int]


def test_comma_separated_string_list():
    m = StrListModel(lst='a,b,c')
    assert m.lst == ['a', 'b', 'c']


def test_comma_separated_int_list():
    m = IntListModel(lst='12,34,567')
    assert m.lst == [12, 34, 567]


def test_comma_separated_int_list_error():
    try:
        IntListModel(lst='12,34,abc')
    except ValidationError as err:
        assert err.errors() == [
            {
                'loc': ('lst', '2'),
                'msg': 'value is not a valid integer',
                'type': 'type_error.integer'
            }
        ]

The tests explain what this code does. However, the models using it do not work with FastAPI, and I currently do not have the time to debug or dive deeper into the issue. The intent was to support query strings like ?company_id__in=1,2,54.