[GitHub] astahlman commented on a change in pull request #4396: [AIRFLOW-3585] - Add edges to database

[GitBox <gi...@apache.org>]

astahlman commented on a change in pull request #4396: [AIRFLOW-3585] - Add edges to database
URL: https://github.com/apache/airflow/pull/4396#discussion_r257084944
 
 

 ##########
 File path: airflow/models/__init__.py
 ##########
 @@ -4012,17 +4088,55 @@ def create_dagrun(self,
             conf=conf,
             state=state
         )
+
+        dag_model = DagModel.get_dagmodel(self.dag_id)
+
+        tis = self.create_tis(execution_date)
+        edges = self.create_edges(-1)
+
+        last_run = dag_model.get_last_dagrun(include_externally_triggered=True)
+        if last_run is None:
+            same = False
+        else:
+            last_edges = DagEdge.fetch_edges_db(self.dag_id, last_run.graph_id)
+
+            # Compare edges from last run
+            same = True
+            if len(last_edges) != len(edges):
 
 Review comment:
   I think this could be expressed more simply as:
   
   ```python
   prev_edges = [(edge.from_task, edge.to_task)
                 for edge in last_edges]
   current_edges = [(edge.from_task, edge.to_task)
                    for edge in edges])
   is_dag_unchanged = len(current_edges) == len(prev_edges)
   is_dag_unchanged &= set(current_edges) == set(prev_edges)
   ```
   If these lists can contain duplicates (don't think they should?) you could even drop the `len()` check.

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