导入 web2py 的 DAL 以与 App Engine 上的 Google Cloud SQL 一起使用答案

【问题标题】：Import web2py's DAL to be used with Google Cloud SQL on App Engine导入 web2py 的 DAL 以与 App Engine 上的 Google Cloud SQL 一起使用
【发布时间】：2012-04-03 17:09:06
【问题描述】：

我想在 App Engine 上构建一个应用，它使用 Cloud SQL 作为后端数据库，而不是 App Engine 自己的数据存储设施（不支持常见的 SQL 操作，例如 JOIN）。

Cloud SQL 有一个 DB-API，因此我一直在寻找一个轻量级的数据抽象层 (DAL) 来帮助轻松操作云数据库。一项小研究表明，web2py 有一个非常简洁的 DAL，它与 Cloud SQL 兼容。

因为我实际上并不需要整个全栈 web2py 框架，所以我将 dal.py 文件从 /gluon 文件夹复制到一个简单的测试应用程序的主目录中，并将这一行包含在我的应用程序中：

from dal import DAL, Field

db=DAL('google:sql://myproject:myinstance/mydatabase')

但是，在我部署应用程序并尝试运行它后，这会产生错误。

Traceback (most recent call last):
  File "/base/python_runtime/python_lib/versions/1/google/appengine/ext/webapp/_webapp25.py", line 701, in __call__
    handler.get(*groups)
  File "/base/data/home/apps/jarod-helloworld/2.357593994022416181/helloworld2.py", line 13, in get
    db=DAL('google:sql://serangoon213home:rainman001/guestbook')
  File "/base/data/home/apps/jarod-helloworld/2.357593994022416181/dal.py", line 5969, in __init__
    raise RuntimeError, "Failure to connect, tried %d times:\n%s" % (attempts, tb)
RuntimeError: Failure to connect, tried 5 times:
Traceback (most recent call last):
  File "/base/data/home/apps/jarod-helloworld/2.357593994022416181/dal.py", line 5956, in __init__
    self._adapter = ADAPTERS[self._dbname](*args)
  File "/base/data/home/apps/jarod-helloworld/2.357593994022416181/dal.py", line 3310, in __init__
    self.folder = folder or '$HOME/'+thread.folder.split('/applications/',1)[1]
  File "/base/python_runtime/python_dist/lib/python2.5/_threading_local.py", line 199, in __getattribute__
    return object.__getattribute__(self, name)
AttributeError: 'local' object has no attribute 'folder'

看起来这是由于语句分配的“文件夹”属性错误

self.folder = folder or '$HOME/'+thread.folder.split('/applications/',1)[1]

有谁知道这个属性有什么作用，我该如何解决这个问题？

【问题讨论】：

标签： python google-app-engine web2py

【解决方案1】：

文件夹是 DAL 构造器中的一个参数。它指向存储 DB (sqlite) 的文件夹。因此，我认为这不是你的问题。我会再次检查连接字符串。

来自 web2py 文档：

The DAL can be used from any Python program simply by doing this:

from gluon import DAL, Field
db = DAL('sqlite://storage.sqlite',folder='path/to/app/databases')
i.e. import the DAL, Field, connect and specify the folder which contains the .table files (the app/databases folder).

To access the data and its attributes we still have to define all the tables we are going to access with db.define_tables(...).

If we just need access to the data but not to the web2py table attributes, we get away without re-defining the tables but simply asking web2py to read the necessary info from the metadata in the .table files:

from gluon import DAL, Field
db = DAL('sqlite://storage.sqlite',folder='path/to/app/databases',
         auto_import=True))
This allows us to access any db.table without need to re-define it.

【讨论】：