Better error message when removing used druid datasource

[maver1ck]

When I'm removing druid datasource which have some slice added I'm getting this error message:
General Error <class 'UnboundLocalError'>

I think it should be something more human readable.

Full stacktrace.

2016-09-19 22:09:37,496:ERROR:flask_appbuilder.models.sqla.interface:Delete record error: local variable 'src_class' referenced before assignment
Traceback (most recent call last):
  File "/home/mbrynski/.local/lib/python3.4/site-packages/Flask_AppBuilder-1.8.1-py3.4.egg/flask_appbuilder/models/sqla/interface.py", line 318, in delete
    self.session.commit()
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/scoping.py", line 157, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/session.py", line 801, in commit
    self.transaction.commit()
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/session.py", line 392, in commit
    self._prepare_impl()
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/session.py", line 372, in _prepare_impl
    self.session.flush()
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/session.py", line 2019, in flush
    self._flush(objects)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/session.py", line 2137, in _flush
    transaction.rollback(_capture_exception=True)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/util/langhelpers.py", line 60, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/util/compat.py", line 186, in reraise
    raise value
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/session.py", line 2101, in _flush
    flush_context.execute()
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/unitofwork.py", line 373, in execute
    rec.execute(self)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/unitofwork.py", line 532, in execute
    uow
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/persistence.py", line 149, in save_obj
    base_mapper, states, uowtransaction
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/persistence.py", line 282, in _organize_states_for_save
    mapper.dispatch.before_update(mapper, connection, state)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/event/attr.py", line 256, in __call__
    fn(*args, **kw)
  File "/home/mbrynski/.local/lib/python3.4/site-packages/SQLAlchemy-1.0.13-py3.4-linux-x86_64.egg/sqlalchemy/orm/events.py", line 614, in wrap
    fn(*arg, **kw)
  File "/home/mbrynski/caravel/caravel/models.py", line 292, in set_perm
    ds = db.session.query(src_class).filter_by(id=int(id_)).first()
UnboundLocalError: local variable 'src_class' referenced before assignment

[maver1ck]

I'll try to work on this today.
This will be my first contribution to Caravel so please be patient.

[maver1ck]

It's not so easy for me.
I tried to do following:

--- a/caravel/models.py
+++ b/caravel/models.py
@@ -289,9 +289,13 @@ def set_perm(mapper, connection, target):  # noqa
     elif target.druid_datasource_id:
         src_class = DruidDatasource
         id_ = target.druid_datasource_id
+    else:
+        flasher("Can't remove {} datasource with active slices".format(target.datasource_name), "danger")
+        return
     ds = db.session.query(src_class).filter_by(id=int(id_)).first()
     target.perm = ds.perm

But result is that I'm getting as many warning as slice count :>

I'm looking deeper into SQL Alchemy ORM (this is trigger on cascade delete)

[xrmx]

Please note that #1078 will change things quite a bit around this code. The correct fix i think would be to add a signal handler for the deletion of SqlaTable or DruidDatasource and block the deletion if there are slices. We are losing the FK so we cannot do that in sqlalchemy.

[maver1ck]

OK.
As #1078 was merged I'm looking into the problem.

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