'Check that all required (combinations) of fields are set.
Also fills in computed properties.
Raises:
InvalidConfiguration: If the config is invalid.'

def CheckInitialized(self):

    super(PropertyEntry, self).CheckInitialized()
    if (not (self.external_name or self.import_template or self.export)):
        raise bulkloader_errors.InvalidConfiguration(('Neither    external_name    nor    import_template    nor    export    specified    for    property    %s.' % self.property))
