Flask SQLAlchemy NOT NULL 约束在主键上失败

Question

我正在尝试在 SQLite 中创建一个数据库，它有两个表，一个用于机场列表，另一个用于这些机场对之间的旅行列表。 我已将其设置为自我参照的多对多关系：

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)

当我打开 Python shell 并导入这些模型时，我让 SQLAlchemy 会话添加 Airport 对象并提交就好了，但是当我执行以下操作时：

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

它给了我这个回溯：

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

上述异常是以下异常的直接原因：

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)]

关键部分似乎是底线：

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)]

看起来是因为我没有给 id 参数赋值，所以它拒绝添加对象。 但我认为这个 id 会自动添加和递增，就像 Airport 对象的 id 参数一样。 我在这里缺少什么？

Answer 1

将显式autoincrement=True添加到 Trips 类定义：

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

如果表是在没有显式 AUTOINCREMENT 的情况下创建的，则需要传递 Trips.id=NULL 以增加它，请参阅https://www.sqlite.org/faq.html#q1

Answer 2

在版本中：SQLAlchemy 1.2.7 Flask-SQLAlchemy 2.3.2 autoincrement=True 不是必需的para，但要小心你的主键定义，因为你已经定义了 'id' 列作为主键，你不应该定义另一个如果不需要，则将列作为主键，否则，您必须在插入记录时自行设置 id 列的值。

Answer 3

我在用作具有附加属性字段的多对多的类映射表中遇到了同样的问题。 出现错误的原因不是因为没有为主键显式定义自动增量，而是因为外键列也有 primary_key = True。 如果没有在模型中设置额外的 primary_keys，这种关系就可以正常工作。