def to_tsv(self, include_readonly=True):
data = self.__dict__<EOL>fields = self.fields(writable=not include_readonly)<EOL>return '<STR_LIT:\t>'.join(field.to_db_string(data[name], quote=False) for name, field in iteritems(fields))<EOL>
Returns the instance's column values as a tab-separated line. A newline is not included.

- `include_readonly`: if false, returns only fields that can be inserted into database.