python - 在 Flask 中使用 SQLAlchemy 创建数据库

Question

我想知道在 Flask 中创建 SQLAlchemy 数据库需要做什么。根据documentation我应该在我的 Flask 应用程序中创建模型，然后转到 Python shell 并使用 db.create_all() 来创建它。但这不起作用。

我的 Flask 应用:

import os
import flask
import settings
from flask_sqlalchemy import SQLAlchemy

app = flask.Flask(__name__)
app.config['SESSION_TYPE'] = 'filesystem'
app.secret_key = os.urandom(24)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:////database.db'
db = SQLAlchemy(app)
(...)

型号:

from app import db

class User(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    username = db.Column(db.String(15), unique = True)
    password = db.Column(db.String(15), unique = True)
    tasks = db.relationship('Task', backref='author', lazy='dynamic')

    def __init__(self, username, password):
        self.username = username
        self.password = password

class Task(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    scene = db.Column(db.String(140), nullable = False)
    state = db.Column(db.Integer(1), nullable = False)
    progress = db.Column(db.Integer(3), nullable = False)
    add_date = db.Column(db.DateTime, nullable = False)
    start_date = db.Column(db.DateTime, nullable = False)
    finish_date = db.Column(db.DateTime, nullable = False)
    rendered_scene = db.Column(db.String(140))
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))

错误代码:

>>> from app import db
>>> db.create_all()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\site-packages\flask_sqlalchemy\__init__.py", line 895, in create_all
    self._execute_for_all_tables(app, bind, 'create_all')
  File "C:\Python27\lib\site-packages\flask_sqlalchemy\__init__.py", line 887, in _execute_for_all_tables
    op(bind=self.get_engine(app, bind), **extra)
  File "C:\Python27\lib\site-packages\sqlalchemy\sql\schema.py", line 3420, in create_all
    tables=tables)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 1727, in_run_visitor
    with self._optional_conn_ctx_manager(connection) as conn:
  File "C:\Python27\lib\contextlib.py", line 17, in __enter__
    return self.gen.next()
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 1720, in_optional_conn_ctx_manager
    with self.contextual_connect() as conn:
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\base.py", line 1910, incontextual_connect
    self.pool.connect(),
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 338, in connect
    return _ConnectionFairy._checkout(self)
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 645, in _checkout
    fairy = _ConnectionRecord.checkout(pool)
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 440, in checkout

    rec = pool._do_get()
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 1058, in _do_get

    return self._create_connection()
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 285, in _create_connection
    return _ConnectionRecord(self)
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 411, in __init__

    self.connection = self.__connect()
  File "C:\Python27\lib\site-packages\sqlalchemy\pool.py", line 539, in __connect
    connection = self.__pool._creator()
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\strategies.py", line 96, in connect
    connection_invalidated=invalidated
  File "C:\Python27\lib\site-packages\sqlalchemy\util\compat.py", line 199, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\strategies.py", line 90, in connect
    return dialect.connect(*cargs, **cparams)
  File "C:\Python27\lib\site-packages\sqlalchemy\engine\default.py", line 377, in connect
    return self.dbapi.connect(*cargs, **cparams)
sqlalchemy.exc.OperationalError: (OperationalError) unable to open database file
 None None

Answer 1

数据库 uri 中的 / 太多了。格式为dialect+driver://user:pass@host:port/db_name。对于 SQLite，db_name 是数据库的路径。您已经指定了绝对路径 /database.db，这意味着您正在尝试在文件系统的根目录中创建数据库。

使用 sqlite:///database.db(相对路径)将在(相对于)当前工作目录中创建数据库。

您可能想要指定一个绝对路径，但要根据项目位置构建它，因为您可以从另一个文件夹运行应用程序。假设您要在与应用设置代码相同的目录中创建数据库，请构建一个相对于 __file__ 的路径。

db_path = os.path.join(os.path.dirname(__file__), 'app.db')
db_uri = 'sqlite:///{}'.format(db_path)
app.config['SQLALCHEMY_DATABASE_URI'] = db_uri