db.close()

在看peewee文档的例子说明时，文档中有这段：
Because sqlite likes to have a separate connection per-thread, we will tell flask that during the request/response cycle we need to create a connection to the database. Flask provides some handy decorators to make this a snap:

@app.before_request
def before_request():
g.db = database
g.db.connect()

@app.after_request
def after_request(response):
g.db.close()
return response

是不是只有用sqlite的时候才需要 db.connect()，然后 db.close呢？
我看其他例子都没见到db.close影子，记得asp+access时随处可见。