Support choices #35

from django.db import models

class Student(models.Model):
    FRESHMAN = 'FR'
    SOPHOMORE = 'SO'
    JUNIOR = 'JR'
    SENIOR = 'SR'
    YEAR_IN_SCHOOL_CHOICES = (
        (FRESHMAN, 'Freshman'),
        (SOPHOMORE, 'Sophomore'),
        (JUNIOR, 'Junior'),
        (SENIOR, 'Senior'),
    )
    year_in_school = models.CharField(
        max_length=2,
        choices=YEAR_IN_SCHOOL_CHOICES,
        default=FRESHMAN,
    )

    def is_upperclass(self):
        return self.year_in_school in (self.JUNIOR, self.SENIOR)

class ChoiceField(ModelField, typesystem.Choice):
    def __init__(self, **kwargs):
        if 'choices' in kwargs:
            choices = kwargs.pop('choices')
            super(typesystem.Choice, self).__init__(choices=choices)
        super().__init__(**kwargs)

class String(ChoiceField, typesystem.String):
     def __init__(self, **kwargs):
        ....
     def validate(self, value, *, strict:bool = False):
        # overload validate
        if self.choices:
            super(typesystem.Choice, self).validate(value)
        return super(typesystem.String, self).validate(value)