BitOptionsField holds a short list of predefined options in a single integer field

bitoptionsfield.py

# -*- coding: utf-8 -*-

from django.db import models
from django.core import exceptions


__all__ = ("BitOptionsField", )


class BitOptionsField(models.Field):
    
    """
    BitOptionsField holds a short list of predefined options
    in a single integer field.
    
    'options' argument is required, it should provide predefined
              list of options
    
    'default' argument is optional, it can provide default list
              of options
    """
    
    __metaclass__ = models.SubfieldBase
    
    def __init__(self, *args, **kwargs):
        if "options" not in kwargs:
            raise RuntimeError("options param is required for BitOptionsField")
        self.options = kwargs.pop("options")
        if "default" in kwargs:
            if not isinstance(kwargs["default"], int):
                kwargs["default"] = self._encode_options(kwargs["default"])
        else:
            kwargs["default"] = 0
        super(BitOptionsField, self).__init__(*args, **kwargs)
    
    def get_internal_type(self):
        return "IntegerField"
    
    def to_python(self, value):
        if type(value) in (int, long):
            return self._decode_options(value)
        return value
    
    def get_db_prep_value(self, value, connection=None, prepared=False):
        if type(value) in (int, long):
            return value
        return self._encode_options(value)

    def _decode_options(self, value):
        opts = []
        for index, option in enumerate(self.options):
            if value & (1 << index):
                opts.append(option)
        return opts

    def _encode_options(self, value):
        int_val = 0
        for option in value:
            if option not in self.options:
                raise exceptions.ValidationError("%s is not valid option" \
                                                 % option)
            int_val += (1 << self.options.index(option))
        return int_val

    def south_field_triple(self):
        from south.modelsinspector import introspector
        field_class = self.__class__.__module__ + "." + self.__class__.__name__
        args, kwargs = introspector(self)
        kwargs["options"] = []
        return (field_class, args, kwargs)