SQL-alchemy: ValueError too many values to unpack?

Question

I have a website running with a mysql database using the sql-alchemy package that has suddenly broken. I have done some research and found that the expected issue is that the newest sql-alchemy update is handing flask-admin one more value than expected from

"cls, key = identity_key(instance=obj)"

Source

The suggested fix is to edit the files to accept a third item but I am unable to do this with the permissions I have on my environment.

Another answer links to a repo on github but I cannot figure out how that helps me. I'm very new to this and I don't know if I am supposed to clone the repo or how exactly to do that if I am.

Any help is appreciated!

Here is the error dump

2018-01-22 20:01:59,593: [2018-01-22 20:01:59,592] ERROR in app: Exception on /reservation/add [GET]
2018-01-22 20:01:59,594: Traceback (most recent call last):
2018-01-22 20:01:59,594:
File "fakepath/flask/app.py", line 1982, in wsgi_app
2018-01-22 20:01:59,594: response = self.full_dispatch_request()2018-01-22 20:01:59,594: File "fakepath/flask/app.py", line 1614, in full_dispatch_request
2018-01-22 20:01:59,594: rv = self.handle_user_exception(e)
2018-01-22 20:01:59,595: File "fakepath/flask/app.py", line 1517, in handle_user_exception2018-01-22 20:01:59,595: reraise(exc_type, exc_value, tb)2018-01-22 20:01:59,595: File "fakepath/flask/_compat.py", line 33, in reraise
2018-01-22 20:01:59,595: raise value2018-01-22 20:01:59,595: File "fakepath/flask/app.py", line 1612, in full_dispatch_request
2018-01-22 20:01:59,595: rv = self.dispatch_request()
2018-01-22 20:01:59,596: File "fakepath/flask/app.py", line 1598, in dispatch_request2018-01-22 20:01:59,596: return self.view_functionsrule.endpoint
2018-01-22 20:01:59,596: File "fakepath/flask_login/utils.py", line 261, in decorated_view
2018-01-22 20:01:59,596: return func(*args, **kwargs)
2018-01-22 20:01:59,597: File "/home/apoalphagammawebmaster/inventory/app/auth/views.py", line 248, in add_reservation
2018-01-22 20:01:59,597: form=form, title='Add Reservation')
2018-01-22 20:01:59,597: File "fakepath/flask/templating.py", line 134, in render_template2018-01-22 20:01:59,597: context, ctx.app)
2018-01-22 20:01:59,597: File "fakepath/flask/templating.py", line 116, in _render
2018-01-22 20:01:59,597: rv = template.render(context)
2018-01-22 20:01:59,598: File "fakepath/jinja2/asyncsupport.py", line 76, in render
2018-01-22 20:01:59,598: return original_render(self, *args, **kwargs)2018-01-22 20:01:59,598: File "fakepath/jinja2/environment.py", line 1008, in render
2018-01-22 20:01:59,598: return self.environment.handle_exception(exc_info, True)
2018-01-22 20:01:59,598: File "fakepath/jinja2/environment.py", line 780, in handle_exception
2018-01-22 20:01:59,599: reraise(exc_type, exc_value, tb)
2018-01-22 20:01:59,599: File "fakepath/jinja2/_compat.py", line 37, in reraise
2018-01-22 20:01:59,599: raise value.with_traceback(tb)
2018-01-22 20:01:59,599: File "/home/apoalphagammawebmaster/inventory/app/templates/auth/reservations/reservation.html", line 2, in top-level template code
2018-01-22 20:01:59,599:
{% extends "base.html" %}
2018-01-22 20:01:59,599: File "/home/apoalphagammawebmaster/inventory/app/templates/base.html", line 48, in top-level template code
2018-01-22 20:01:59,600: {% block body %}
2018-01-22 20:01:59,600: File "/home/apoalphagammawebmaster/inventory/app/templates/auth/reservations/reservation.html", line 27, in block "body"
2018-01-22 20:01:59,600: {{ wtf.quick_form(form) }}
2018-01-22 20:01:59,600: File "fakepath/jinja2/runtime.py", line 579, in _invoke
2018-01-22 20:01:59,600: rv = self._func(*arguments)
2018-01-22 20:01:59,601: File "fakepath/flask_bootstrap/templates/bootstrap/wtf.html", line 205, in template
2018-01-22 20:01:59,601: {{ form_field(field,2018-01-22 20:01:59,601: File "fakepath/jinja2/runtime.py", line 579, in _invoke
2018-01-22 20:01:59,601: rv = self._func(*arguments)
2018-01-22 20:01:59,601: File "fakepath/flask_bootstrap/templates/bootstrap/wtf.html", line 123, in template
2018-01-22 20:01:59,601:
{{field(class="form-control", **kwargs)|safe}}
2018-01-22 20:01:59,601: File "fakepath/wtforms/fields/core.py", line 153, in call
2018-01-22 20:01:59,601: return self.meta.render_field(self, kwargs)
2018-01-22 20:01:59,602:
File "fakepath/wtforms/meta.py", line 56, in render_field2018-01-22 20:01:59,602: return field.widget(field, **render_kw)
2018-01-22 20:01:59,602: File "fakepath/wtforms/widgets/core.py", line 287, in call2018-01-22 20:01:59,602: for val, label, selected in field.iter_choices():
2018-01-22 20:01:59,602: File "fakepath/wtforms/ext/sqlalchemy/fields.py", line 107, in iter_choices
2018-01-22 20:01:59,602: for pk, obj in self._get_object_list():
2018-01-22 20:01:59,602: File "fakepath/wtforms/ext/sqlalchemy/fields.py", line 100, in _get_object_list
2018-01-22 20:01:59,602: self._object_list = list((text_type(get_pk(obj)), obj) for obj in query)
2018-01-22 20:01:59,603: File "fakepath/wtforms/ext/sqlalchemy/fields.py", line 100, in
2018-01-22 20:01:59,603: self._object_list = list((text_type(get_pk(obj)), obj) for obj in query)
2018-01-22 20:01:59,603: File "fakepath/wtforms/ext/sqlalchemy/fields.py", line 189, in get_pk_from_identity
2018-01-22 20:01:59,603: cls, key = identity_key(instance=obj)
2018-01-22 20:01:59,603: ValueError: too many values to unpack (expected 2)

Answer 1

The problem is covered on the github issues thread - https://github.com/flask-admin/flask-admin/issues/1588

Basically, the flask-admin pip package is out of date, in regards the latest sqlalchemy pip package. In that specific area,

cls, key = identity_key(instance=obj)

sqlalchemy is now returning 3 objects, but flask-admin is only expecting 2, hence the error.

The real solution for this is to wait until a new flask-admin version is uploaded to pip, until then, you've a few options.

1. Manually go in and edit that fields.py file
2. As detailed in that issues thread, limit sqlalchemy to version 1.2.0b3. You can do this in your requirements.txt file, or manually with a pip upgrade install, pip install --upgrade sqlalchemy==1.2.0b3
3. As the fix is in flask-admin's master branch in their github repository, install that version of flask-admin with the pip location of git+https://github.com/flask-admin/flask-admin. Again, you do this in your requirements.txt file, or with a pip upgrade install, pip install --upgrade git+https://github.com/flask-admin/flask-admin.

My personal preference, and what I've done, is option 3. If you look through the code itself, it's a line the maintainers want to remove, anyway, and how they're dealing with it is better, and in general with these things, I prefer to go forward (latest version of flask-admin) rather than holding things back (rollback sqlalchemy to a previous version), and certainly better than manually editing the raw code.

Answer 2

I was also having this issue. I got the hacks (as described above) to work, but looking at the discussions on https://github.com/wtforms/wtforms/issues/373 and https://github.com/flask-admin/flask-admin/issues/1588, it looked like support for wtforms_sqlalchemy is not as good as wtforms_alchemy.

So, I installed wtforms_alchemy

pip install wtforms_alchemy 

and replaced wtforms_sqlalchemy with wtform_alchemy in my project

from wtforms_alchemy.fields import QuerySelectField 

and my project worked the same.