烧瓶中的 sqlalchemy.orm.exc.UnmappedInstanceError [英] sqlalchemy.orm.exc.UnmappedInstanceError in flask

问题描述

我一直在阅读 SQLAlchemy 文档，但我不理解它们.错误 (UnmappedInstanceError) 表示未映射某些内容.什么没有映射?我真的不明白 sqlalchemy，我想回去使用裸 SQLite，但是这么多人推荐这个，所以我想我应该学习它.这是回溯:

I have been reading the SQLAlchemy docs, but I don't understand them. The error (UnmappedInstanceError) says something isn't mapped. What isn't mapped? I really don't get sqlalchemy and I want to go back to using naked sqlite, but so many people recommend this, so I thought I should learn it. Here is the traceback:

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1836, in __call__
return self.wsgi_app(environ, start_response)

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1820, in wsgi_app
response = self.make_response(self.handle_exception(e))

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1403, in handle_exception
reraise(exc_type, exc_value, tb)

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1817, in wsgi_app
response = self.full_dispatch_request()

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1477, in full_dispatch_request
rv = self.handle_user_exception(e)

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1381, in handle_user_exception
reraise(exc_type, exc_value, tb)

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1475, in full_dispatch_request
rv = self.dispatch_request()

File "C:UsersMe
eposmandjvenvlibsite-packagesflaskapp.py", line 1461, in dispatch_request
return self.view_functions[rule.endpoint](**req.view_args)

File "C:UsersMe
eposmandj2appviews.py", line 170, in add_manentry
db.session.add(q)

File "C:UsersMe
eposmandjvenvlibsite-packagessqlalchemyormscoping.py", line 149, in do
return getattr(self.registry(), name)(*args, **kwargs)

File "C:UsersMe
eposmandjvenvlibsite-packagessqlalchemyormsession.py", line 1452, in add
raise exc.UnmappedInstanceError(instance)

UnmappedInstanceError: Class '__builtin__.unicode' is not mapped

这是适用的代码:

@app.route('/addm', methods=['POST'])
def add_mentry():
    if not session.get('logged_in'):
        abort(401)
    form = MForm(request.form)
    filename = ""
    if request.method == 'POST':
        cover = request.files['cover']
        if cover and allowed_file(cover.filename):
            filename = secure_filename(cover.filename)
            cover = cover.save(os.path.join(app.config['UPLOAD_FOLDER'], filename))

    q = request.form['name']
    # do for 12 more fields
    db.session.add(q)
    db.session.commit()
    flash('New entry was successfully posted')
    return redirect(url_for('moutput'))

推荐答案

q = request.form['name']
# do for 12 more fields
db.session.add(q)

request.form['name'] 将返回一个 unicode 值.那么，你...

request.form['name'] will return a unicode value. Then, you do...

db.session.add(q)

会话的目标是跟踪实体(Python 对象)，而不是像您试图这样做的单个 unicode 值(参见 此处 了解有关会话的更多信息).因此，您应该添加具有映射的对象(例如 "映射" 部分 ORM 教程)，但您实际上传递的是一个简单的 unicode 值

The goal of the session is to keep track of Entities (Python objects), not individual unicode values as you seem to be trying to do it (See here for more on what the session does). Thus, you should be adding objects that have a mapping (such as a User object as shown in the "Mapping" section of the ORM tutorial), but you're actually passing a simple unicode value

您使用的只是 SQLAlchemy 的一部分:ORM(对象关系映射器).ORM 会尝试做一些事情，比如允许你创建一个新的 python 对象，并通过将对象添加"到会话中来自动生成 SQL..

What you're using is just one part of SQLAlchemy: the ORM (Object-Relational Mapper). The ORM will try to do things like allow you to create a new python object and have the SQL automatically generaeted by "adding" the object to the session..

a = MyEntity()
session.add(a)
session.commit() # Generates SQL to do an insert for the table that MyEntity is for

请记住，您可以在不使用 ORM 功能的情况下使用 SQLAlchemy.你可以只做 db.execute('INSERT...', val1, val2) 来替换你已经裸"的 SQL.SQLAlchemy 将为您提供连接池等(尽管如果您使用 SQLite，您可能不关心连接池).

Keep in mind that you can use SQLAlchemy without using the ORM functionality. You could just do db.execute('INSERT...', val1, val2) to replace your already "naked" SQL. SQLAlchemy will provide you connection pooling, etc (although if you're using SQLite, you probably don't care about connection pooling).

如果您想了解 Flask-SQLAlchemy，我首先建议您通过使用简单的脚本(如 教程.然后您将了解 Flask-SQLAlchemy 如何使用它.

If you want to understand Flask-SQLAlchemy, I would first recommend understanding how SQLAlchemy works (especially the ORM side) by trying it out using simple scripts (as shown in the tutorials. Then you'll understand how Flask-SQLAlchemy would work with it.

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