MSSQL UUID Field compatible for the django-jsonfield app. It makes migrations from POstgres to MSSQL work :)

mssql_fields.py

from uuidfield.fields import StringUUID
from django.utils.encoding import smart_unicode

__author__ = 'danigosa'

from uuidfield import UUIDField

class MssqlUUIDField(UUIDField):
    """
    A field which stores a UUID value in hex format. This may also have
    the Boolean attribute 'auto' which will set the value on initial save to a
    new UUID value (calculated using the UUID1 method). Note that while all
    UUIDs are expected to be unique we enforce this with a DB constraint.
    """
    def __init__(self, version=4, node=None, clock_seq=None,
                 namespace=None, name=None, auto=False, *args, **kwargs):
        assert version in (1, 3, 4, 5), "UUID version %s is not supported." % version
        self.auto = auto
        self.version = version
        # We store UUIDs in hex format, which is fixed at 32 characters.
        # MSSQL UUIDs as TEXT: we put 36 chars to enable migration from Postgresql UUID
        kwargs['max_length'] = 36
        if auto:
            # Do not let the user edit UUIDs if they are auto-assigned.
            kwargs['editable'] = False
            kwargs['blank'] = True
            kwargs['unique'] = True
        if version == 1:
            self.node, self.clock_seq = node, clock_seq
        elif version in (3, 5):
            self.namespace, self.name = namespace, name
        super(UUIDField, self).__init__(*args, **kwargs)

    def to_python(self, value):
        """
        Returns a ``StringUUID`` instance from the value returned by the
        database. This doesn't use uuid.UUID directly for backwards
        compatibility, as ``StringUUID`` implements ``__unicode__`` with
        ``uuid.UUID.hex()``.
            """
        if not value:
            return None
            # attempt to parse a UUID including cases in which value is a UUID
        # instance already to be able to get our StringUUID in.
        #FIX: Must strip string because it adds 4 spaces to fill the length
        return StringUUID(smart_unicode(value.strip()))