Detached instance in tasks controller

[roscisz]

Subject of the issue

Describe your issue here.

Your environment

List relevant info:

• TensorHive 0.3.3

Steps to reproduce

Assign some tasks to a reservation in the calendar view. Then repeat: assign the same tasks to the same reservation.

Expected behaviour

Re-assagning tasks should not be possible while the tasks are running.

Actual behaviour

ERROR | 2020-11-03 16:20:28 | MainThread | MSG: Exception on /api/0.3/tasks [GET] | FROM: tensorhive.api.APIServer
Traceback (most recent call last):
File "/home/tensorhive/venv/lib/python3.6/site-packages/tensorhive/controllers/task.py", line 167, in get_all
content, status = business_get_all(user_id, sync_all)
File "/home/tensorhive/venv/lib/python3.6/site-packages/tensorhive/controllers/task.py", line 275, in business_get_all
synchronize(task.id)
File "/home/tensorhive/venv/lib/python3.6/site-packages/sqlalchemy/orm/attributes.py", line 276, in get
return self.impl.get(instance_state(instance), dict_)
File "/home/tensorhive/venv/lib/python3.6/site-packages/sqlalchemy/orm/attributes.py", line 677, in get
value = state._load_expired(state, passive)
File "/home/tensorhive/venv/lib/python3.6/site-packages/sqlalchemy/orm/state.py", line 660, in _load_expired
self.manager.deferred_scalar_loader(self, toload)
File "/home/tensorhive/venv/lib/python3.6/site-packages/sqlalchemy/orm/loading.py", line 913, in load_scalar_attributes
"attribute refresh operation cannot proceed" % (state_str(state))
sqlalchemy.orm.exc.DetachedInstanceError: Instance <Task at 0x7f1ef437bac8> is not bound to a Session; attribute refresh operation cannot proceed (Background on this error at: http://sqlalche.me/e/bhk3)

[roscisz]

could be a duplicate of #174