Using a 2.0.0 beta 2 build...

![Untitled](https://user-images.githubusercontent.com/4283/99546252-3ebe1a80-2984-11eb-9681-8d6e718b22c5.gif)

Log from webserver:

```
[2020-11-18 14:58:52,712] {interface.py:713} ERROR - Delete record error: Dependency rule tried to blank-out primary key column 'job.id' on instance '<SchedulerJob at 0x7fc68ba7f990>'
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/flask_appbuilder/models/sqla/interface.py", line 698, in delete
    self.session.commit()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/scoping.py", line 163, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 1042, in commit
    self.transaction.commit()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 504, in commit
    self._prepare_impl()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 483, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 2536, in flush
    self._flush(objects)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 2678, in _flush
    transaction.rollback(_capture_exception=True)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/langhelpers.py", line 70, in __exit__
    with_traceback=exc_tb,
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/util/compat.py", line 182, in raise_
    raise exception
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/session.py", line 2638, in _flush
    flush_context.execute()
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/unitofwork.py", line 422, in execute
    rec.execute(self)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/unitofwork.py", line 538, in execute
    self.dependency_processor.process_deletes(uow, states)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/dependency.py", line 547, in process_deletes
    state, child, None, True, uowcommit, False
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/dependency.py", line 604, in _synchronize
    sync.clear(dest, self.mapper, self.prop.synchronize_pairs)
  File "/usr/local/lib/python3.7/site-packages/sqlalchemy/orm/sync.py", line 88, in clear
    "column '%s' on instance '%s'" % (r, orm_util.state_str(dest))
AssertionError: Dependency rule tried to blank-out primary key column 'job.id' on instance '<SchedulerJob at 0x7fc68ba7f990>'
172.19.0.1 - - [18/Nov/2020:14:58:52 +0000] "POST /dagrun/delete/147 HTTP/1.1" 302 415 "http://localhost:8080/dagrun/list/?_flt_3_dag_id=airflow_community_data_refresh&_flt_3_state=success" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/86.0.4240.193 Safari/537.36"
```
airflow/models/serialized_dag.py
"""A table for serialized DAGs.
    serialized_dag table is a snapshot of DAG files synchronized by scheduler.
    This feature is controlled by:
    * ``[core] min_serialized_dag_update_interval = 30`` (s):
      serialized DAGs are updated in DB when a file gets processed by scheduler,
      to reduce DB write rate, there is a minimal interval of updating serialized DAGs.
    * ``[scheduler] dag_dir_list_interval = 300`` (s):
      interval of deleting serialized DAGs in DB when the files are deleted, suggest
      to use a smaller interval such as 60
    It is used by webserver to load dags
    because reading from database is lightweight compared to importing from files,
    it solves the webserver scalability issue.
    """
    __tablename__ = 'serialized_dag'
    dag_id = Column(String(ID_LEN), primary_key=True)
    fileloc = Column(String(2000), nullable=False)
    
    fileloc_hash = Column(BigInteger, nullable=False)
    data = Column(sqlalchemy_jsonfield.JSONField(json=json), nullable=False)
    last_updated = Column(UtcDateTime, nullable=False)