[GitHub] [airflow] Fokko commented on a change in pull request #6370: AIRFLOW-5701: Don't clear xcom explicitly before execution

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Fokko commented on a change in pull request #6370: AIRFLOW-5701: Don't clear xcom explicitly before execution
URL: https://github.com/apache/airflow/pull/6370#discussion_r339292407
 
 

 ##########
 File path: airflow/models/xcom.py
 ##########
 @@ -43,16 +43,14 @@ class XCom(Base, LoggingMixin):
     """
     __tablename__ = "xcom"
 
-    id = Column(Integer, primary_key=True)
-    key = Column(String(512))
+    key = Column(String(512), primary_key=True, nullable=False)
     value = Column(LargeBinary)
-    timestamp = Column(
-        UtcDateTime, default=timezone.utcnow, nullable=False)
-    execution_date = Column(UtcDateTime, nullable=False)
+    timestamp = Column(UtcDateTime, default=timezone.utcnow, nullable=False)
+    execution_date = Column(UtcDateTime, primary_key=True, nullable=False)
 
     # source information
-    task_id = Column(String(ID_LEN), nullable=False)
-    dag_id = Column(String(ID_LEN), nullable=False)
+    task_id = Column(String(ID_LEN), primary_key=True, nullable=False)
+    dag_id = Column(String(ID_LEN), primary_key=True, nullable=False)
 
     __table_args__ = (
         Index('idx_xcom_dag_task_date', dag_id, task_id, execution_date, unique=False),
 
 Review comment:
   Yes, you're right. The index has been replaced by the PR.
   
   - For sqlite the only way of doing these kinds of changes is dropping and recreating the table. Because sqlite does not have any support for altering columns. 
   - The table is actually more or less the same, only the ID column is removed (which wasn't being used).
   - I looked at other `__table_args__`, and I don't see a `PrimaryKeyConstraint` being defined. I think it would make sense to add this.

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