def _get_flat_db_sources(self, model):
        sources = []
        for source in self.sources:
            for sub_source in self.expand_source(source):
                target_field = self.resolve_source(model, sub_source)
                if target_field:
                    sources.append(sub_source)
        return sources
Return a flattened representation of the individual ``sources`` lists.
dataset/ETHPy150Open pivotal-energy-solutions/django-datatable-view/datatableview/columns.py/CompoundColumn._get_flat_db_sources