Flask 和 SQLAlchemy db.session.commit 不工作

Question

当我向表中添加测试用户时User，它添加得很好，即使我执行时也很好db.session.add(u)，但当我执行时它会抛出错误db.session.commit()。

from app import db

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Integer(120), unique=True)
    email = db.Column(db.Integer(120), unique=True)
    configkey = db.Column(db.Integer(200), unique=True)
    dob = db.Column(db.DateTime)
    country = db.Column(db.Integer(120))
    friends = db.relationship('Friend', backref = 'friendof', lazy = 'dynamic')


    def __repr__(self):
        return '<User %r>' % (self.name)

class Friend(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    name = db.Column(db.Integer(120), unique=True)
    email = db.Column(db.Integer(120), unique=True)
    dob = db.Column(db.DateTime)
    country = db.Column(db.Integer(120))
    lastmessage = db.Column(db.Integer(1500))
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))


    def __repr__(self):
        return '<FriendName %r>' % (self.name)

--编辑，包括Python控制台中的错误消息：

>>> u = models.User(name="sd", email="e")                                                                                                                      
>>> db.session.add(u)
>>> db.session.commit()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/scoping.py", line 149, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 721, in commit
    self.transaction.commit()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 354, in commit
    self._prepare_impl()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 334, in _prepare_impl
    self.session.flush()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1818, in flush
    self._flush(objects)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1936, in _flush
    transaction.rollback(_capture_exception=True)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/langhelpers.py", line 58, in __exit__
    compat.reraise(exc_type, exc_value, exc_tb)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1900, in _flush
    flush_context.execute()
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 372, in execute
    rec.execute(self)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 525, in execute
    uow
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 64, in save_obj
    table, insert)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/persistence.py", line 569, in _emit_insert_statements
    execute(statement, params)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 662, in execute
    params)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 761, in _execute_clauseelement
    compiled_sql, distilled_params
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 874, in _execute_context
    context)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1024, in _handle_dbapi_exception
    exc_info
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/util/compat.py", line 196, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 867, in _execute_context
    context)
  File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 324, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.OperationalError: (OperationalError) no such table: user u'INSERT INTO user (name, email, configkey, dob, country) VALUES (?, ?, ?, ?, ?)' ('sd'
, 'e', None, None, None)

Answer 1

我正在查看您的堆栈跟踪（特别是最后一行），看起来您的表尚不存在。

在将新模型与数据库一起使用之前，表和列必须存在。好消息是 SQLAlchemy 可以为您做到这一点。

尝试从程序中的任何位置调用以下命令：

# Creates the schema on the database
db.create_all()

完成后请务必将其删除！

理想情况下，您应该有一个从命令行调用的另一个文件，该文件导入您的 Flask 应用程序，然后运行此命令。例如...

# Replace these with your main file and the name of your flask object
from myapp import app 
# And this one with the name of your database file and object
from database import db 

db.create_all()

print "Database ready!"

编辑：
该db.create_all()命令不会修改现有表，同样，运行后表不会自动更改自身db.create_all()。但是，例如，您可以创建一个新表，然后重新运行该函数并使其显示。

为了正确处理数据库的升级，我建议查看Flask-Migrate，特别是如果您的应用程序最终将在生产环境中使用。

我在初始开发过程中使用的快速而肮脏的方法是删除数据库，如果更改太大，则重新创建数据库。