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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def dag(self) -> Tuple[Dict, Dict]: """Construct the DAG of this pipeline run based on the its operation runs and their downstream. """

        from pipelines import dags

        operation_runs = self.operation_runs.all().prefetch_related('downstream_runs')

        def get_downstream(op_run):
            return op_run.downstream_runs.values_list('id', flat=True)

        return dags.get_dag(operation_runs, get_downstream)