houqp commented on a change in pull request #13278:
URL: https://github.com/apache/airflow/pull/13278#discussion_r547757953



##########
File path: airflow/utils/types.py
##########
@@ -16,8 +16,31 @@
 # under the License.
 import enum
 
+from sqlalchemy.types import TypeDecorator, String
 
-class DagRunType(str, enum.Enum):
+
+class EnumString(TypeDecorator):
+    """
+    Declare db column with this type to make the column compatible with string
+    and string based enum values when building the sqlalchemy ORM query. It can
+    be used just like sqlalchemy.types.String, for example:
+
+    ```
+    class Table(Base):
+        __tablename__ = "t"
+        run_type = Column(EnumString(50), nullable=False)
+    ```
+    """
+    impl = String
+
+    def process_bind_param(self, value, dialect):
+        if isinstance(value, enum.Enum):
+            return value.value
+        else:
+            return value
+
+
+class DagRunType(enum.Enum):

Review comment:
       @ashb i removed the str here to avoid this type being misused in the 
rest of the code base. For example, if `DagRunType.SCHEDULED` is used for 
column types that are not declared as `EnumString`, developer will get the 
incorrect behavior regardless of which db driver is being used, so we can 
surface the issue sooner. That way, it's less likely to get half working PR 
merged into master.




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