query for true instead of querying the object

airflow/models/dagcode.py

@@ -20,6 +20,7 @@
 from datetime import datetime
 
 from sqlalchemy import BigInteger, Column, String, UnicodeText, and_
+from sqlalchemy.sql.expression import literal
 
 from airflow.exceptions import AirflowException, DagCodeNotFound
 from airflow.models import Base
@@ -160,7 +161,7 @@ def has_dag(cls, fileloc, session=None):
         :param session: ORM Session
         """
         fileloc_hash = cls.dag_fileloc_hash(fileloc)
-        return session.query(cls).filter(cls.fileloc_hash == fileloc_hash)\
+        return session.query(literal(True)).filter(cls.fileloc_hash == fileloc_hash)\
             .first() is not None
 
     @classmethod

airflow/models/serialized_dag.py

@@ -25,6 +25,7 @@
 
 import sqlalchemy_jsonfield
 from sqlalchemy import BigInteger, Column, Index, String, and_
+from sqlalchemy.sql.expression import literal
 
 from airflow.models.base import ID_LEN, Base
 from airflow.models.dag import DAG
@@ -92,7 +93,7 @@ def write_dag(cls,
         # If Yes, does nothing
         # If No or the DAG does not exists, updates / writes Serialized DAG to DB
         if min_update_interval is not None:
-            if session.query(cls).filter(
+            if session.query(literal(True)).filter(
                 and_(cls.dag_id == dag.dag_id,
                      (timezone.utcnow() - timedelta(seconds=min_update_interval)) < cls.last_updated)
             ).first() is not None:
@@ -177,7 +178,7 @@ def has_dag(cls, dag_id, session=None):
         :param session: ORM Session
         :rtype: bool
         """
-        return session.query(cls).filter(cls.dag_id == dag_id).first() is not None
+        return session.query(literal(True)).filter(cls.dag_id == dag_id).first() is not None
 
     @classmethod
     @db.provide_session