Flask SQLAlchemy NOT NULL vincolo non riuscito sulla chiave primaria

Question

Sto provando a creare un database in SQLite che ha due tabelle, una per un elenco di aeroporti e un'altra per un elenco di viaggi tra coppie di quegli aeroporti. Ho impostato in su come un auto-referenziale, molti-a-molti:

class Trips(db.Model): 

    __tablename__ = 'trips' 

    id = db.Column(db.Integer, primary_key=True) 
    airport_from = db.Column(db.Integer, db.ForeignKey('airport.id')) 
    airport_to = db.Column(db.Integer, db.ForeignKey('airport.id')) 
    price = db.Column(db.Float) 
    date = db.Column(db.Date) 

class Airport(db.Model): 

    __tablename__ = 'airport' 

    id = db.Column(db.Integer, primary_key=True) 
    iata = db.Column(db.String(8), index=True, unique=True) 
    name = db.Column(db.String(120), index=True, unique=True) 
    city = db.Column(db.String(120)) 
    region = db.Column(db.String(120)) 
    country = db.Column(db.String(120)) 

    flying_from = db.relationship('Trips', backref='end', primaryjoin=(id==Trips.airport_to)) 
    flying_to = db.relationship('Trips', backref='start', primaryjoin=(id==Trips.airport_from)) 

    def __repr__(self): 
     return '<Airport: {0}; IATA: {1}>'.format(self.name, self.iata) 

Quando ho aperto il mio guscio Python e importare questi modelli, ho la sessione SQLAlchemy aggiungere oggetti aeroportuali e impegnarsi più che bene , ma quando faccio qualcosa di simile:

>>> t = models.Trips(airport_from=3, airport_to=4, price=230.0) 
>>> db.session.add(t) 
>>> db.session.commit() 

mi dà questo traceback:

Traceback (most recent call last): 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1139, in _execute_context 
context) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/default.py", line 450, in do_execute 
cursor.execute(statement, parameters) 
sqlite3.IntegrityError: NOT NULL constraint failed: trips.id 

Quanto sopra eccezione è stata la causa diretta della seguente eccezione:

Traceback (most recent call last): 
    File "<stdin>", line 1, in <module> 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/scoping.py", line 150, in do 
    return getattr(self.registry(), name)(*args, **kwargs) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 813, in commit 
    self.transaction.commit() 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 392, in commit 
    self._prepare_impl() 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 372, in _prepare_impl 
    self.session.flush() 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 2027, in flush 
    self._flush(objects) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 2145, in _flush 
    transaction.rollback(_capture_exception=True) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/util/langhelpers.py", line 60, in __exit__ 
    compat.reraise(exc_type, exc_value, exc_tb) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/util/compat.py", line 183, in reraise 
    raise value 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/session.py", line 2109, in _flush 
    flush_context.execute() 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/unitofwork.py", line 373, in execute 
    rec.execute(self) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/unitofwork.py", line 532, in execute 
    uow 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/persistence.py", line 174, in save_obj 
    mapper, table, insert) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/orm/persistence.py", line 800, in _emit_insert_statements 
    execute(statement, params) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 914, in execute 
    return meth(self, multiparams, params) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/sql/elements.py", line 323, in _execute_on_connection 
    return connection._execute_clauseelement(self, multiparams, params) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1010, in _execute_clauseelement 
    compiled_sql, distilled_params 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1146, in _execute_context 
    context) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1341, in _handle_dbapi_exception 
    exc_info 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/util/compat.py", line 189, in raise_from_cause 
    reraise(type(exception), exception, tb=exc_tb, cause=exc_value) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/util/compat.py", line 182, in reraise 
    raise value.with_traceback(tb) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/base.py", line 1139, in _execute_context 
    context) 
    File "/Users/heli/nomad/flask/lib/python3.4/site-packages/sqlalchemy/engine/default.py", line 450, in do_execute 
    cursor.execute(statement, parameters) 
sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) NOT NULL constraint failed: trips.id [SQL: 'INSERT INTO trips (airport_from, airport_to, price, date) VALUES (?, ?, ?, ?)'] [parameters: (3, 4, 230.0, None)] 

La parte fondamentale sembra essere la linea di fondo:

sqlalchemy.exc.IntegrityError: (sqlite3.IntegrityError) NOT NULL constraint failed: trips.id [SQL: 'INSERT INTO trips (airport_from, airport_to, price, date) VALUES (?, ?, ?, ?)'] [parameters: (3, 4, 230.0, None)] 

Sembra, perché non ho dato un valore al parametro id, che è rifiutato di aggiungere l'oggetto. Ma ho pensato che questo ID sarebbe stato automaticamente aggiunto e incrementato, come è successo con il parametro id degli oggetti Airport. Cosa mi manca qui?

Answer 1

Aggiungi esplicito autoincrement=True Trips definizione di classe:

id = db.Column(db.Integer, primary_key=True, autoincrement=True) 

Se tabella viene creata senza AUTOINCREMENT esplicito, è necessario passare Trips.id = NULL al fine di incrementarlo, vedere https://www.sqlite.org/faq.html#q1