>>> from app.models import User, Post
>>> u = User(username='john', email='john@example.com')
>>> db.session.add(u)
>>> db.session.commit()
Traceback (most recent call last):
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2138, in _wrap_pool_connect
    return fn()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 387, in connect
    return _ConnectionFairy._checkout(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 766, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 516, in checkout
    rec = pool._do_get()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1229, in _do_get
    return self._create_connection()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 333, in _create_connection
    return _ConnectionRecord(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 461, in __init__
    self.__connect(first_connect_check=True)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 651, in __connect
    connection = pool._invoke_creator(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 105, in connect
    return dialect.connect(*cargs, **cparams)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 393, in connect
    return self.dbapi.connect(*cargs, **cparams)
sqlite3.OperationalError: unable to open database file

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/scoping.py", line 157, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 874, in commit
    self.transaction.commit()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 461, in commit
    self._prepare_impl()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 441, in _prepare_impl
    self.session.flush()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 2139, in flush
    self._flush(objects)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 2259, in _flush
    transaction.rollback(_capture_exception=True)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 187, in reraise
    raise value
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 2223, in _flush
    flush_context.execute()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/unitofwork.py", line 389, in execute
    rec.execute(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/unitofwork.py", line 548, in execute
    uow
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 156, in save_obj
    base_mapper, states, uowtransaction
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 279, in _organize_states_for_save
    states):
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/persistence.py", line 1094, in _connections_for_states
    connection = uowtransaction.transaction.connection(base_mapper)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 294, in connection
    return self._connection_for_bind(bind, execution_options)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 392, in _connection_for_bind
    conn = self._parent._connection_for_bind(bind, execution_options)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/orm/session.py", line 403, in _connection_for_bind
    conn = bind.contextual_connect()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2103, in contextual_connect
    self._wrap_pool_connect(self.pool.connect, None),
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2142, in _wrap_pool_connect
    e, dialect, self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1456, in _handle_dbapi_exception_noconnection
    exc_info
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 186, in reraise
    raise value.with_traceback(tb)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 2138, in _wrap_pool_connect
    return fn()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 387, in connect
    return _ConnectionFairy._checkout(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 766, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 516, in checkout
    rec = pool._do_get()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 1229, in _do_get
    return self._create_connection()
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 333, in _create_connection
    return _ConnectionRecord(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 461, in __init__
    self.__connect(first_connect_check=True)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/pool.py", line 651, in __connect
    connection = pool._invoke_creator(self)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/strategies.py", line 105, in connect
    return dialect.connect(*cargs, **cparams)
  File "/home/nathan/code/envs/nc/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 393, in connect
    return self.dbapi.connect(*cargs, **cparams)
sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) unable to open database file