问题
Hi I am building a web application using Flask and Sqlite3. I had issues with connecting the database for a while and it did not work when I wrote this:
#version 1
app.config['SQLALCHEMY_DATABASE_URI'] =
'sqlite:////C:/Users/Giang/PyCharmProjects/FlaskWebBlog/FlaskWebBlog/site.db'
Python gave me operational error: can not open database because I wrote with 4 slashes after the colon. After reading sqlalchemy documentation and doing so many trials, I found out this worked:
#with 3 slashes, version 2
app.config['SQLALCHEMY_DATABASE_URI'] =
'sqlite:///C:/Users/Giang/PyCharmProjects/FlaskWebBlog/FlaskWebBlog/site.db'
or this with 4 slashes but no C:
#version 3
app.config['SQLALCHEMY_DATABASE_URI'] =
'sqlite:////Users/Giang/PyCharmProjects/FlaskWebBlog/FlaskWebBlog/site.db'
I am confused because based on the documentation of connecting strings: The file specification for the SQLite database is taken as the “database” portion of the URL. Note that the format of a SQLAlchemy url is:
driver://user:pass@host/database
This means that the actual filename to be used starts with the characters to the right of the third slash. So connecting to a relative filepath looks like:
# relative path
e = create_engine('sqlite:///path/to/database.db')
An absolute path, which is denoted by starting with a slash, means you need four slashes:
# absolute path
e = create_engine('sqlite:////path/to/database.db')
SO according to this, if I use absolute path, I need 4 slashes, but when I did that with version 1, python gave me errors. And when I used 3 slashes for absolute path in version 2, it worked.
So I am really confused. Can anyone explain for me why ? I would really appreciate it. Thank you
回答1:
You are correct about the database
component being read as all the characters after the third slash. Here's the parsed: version 1 URL
>>> import sqlalchemy.engine.url as url
>>> url.make_url('sqlite:////C:/Users/Giang/PyCharmProjects/FlaskWebBlog/FlaskWebBlog/site.db')
sqlite:////C:/Users/Giang/PyCharmProjects/FlaskWebBlog/FlaskWebBlog/site.db
>>> vars(_)
{'drivername': 'sqlite',
'username': None,
'password_original': None,
'host': None,
'port': None,
'database': '/C:/Users/Giang/PyCharmProjects/FlaskWebBlog/FlaskWebBlog/site.db',
'query': {}}
In Windows, a slash at the beginning of a path gets normalized to "the root drive of the current working directory". Using pywin32, we can call GetFullPathName to view the normalized version of a path:
>>> import os
>>> import win32file
>>> os.getcwd()
'C:\\Users\\they4kman'
>>> win32file.GetFullPathName('/C:/test')
'C:\\C:\\test'
>>> win32file.GetFullPathName('/test')
'C:\\test'
>>> win32file.GetFullPathName('C:/test')
'C:\\test'
The reason version 1 doesn't work is because specifying both a leading slash and a drive letter will get normalized by Windows into an invalid path. (More specifically, the path is invalid because colons are not allowed in Windows paths, except at the beginning as a drive specifier.)
To show how a leading slash is normalized differently depending on the environment, let's change the current working directory to one on another drive and check out the normalized path:
>>> os.chdir('D:/')
>>> os.getcwd()
'D:\\'
>>> win32file.GetFullPathName('/test')
'D:\\test'
>>> win32file.GetFullPathName('C:/test')
'C:\\test'
来源:https://stackoverflow.com/questions/56416437/confusion-about-uri-path-to-configure-sqlite-database