BaseModelView.index_view() got an unexpected keyword argument 'cls'

Question

I am trying to build a Flask app with Flask_security_too and Flask_admin. I need to have 1 user linked to 1 Device, but 1 device can have multiple releases:

class Users(db.Model, UserMixin):
    __tablename__ = "users"
    user_id = Column(Integer, primary_key=True)
    username = Column(String(100), unique=True, index=True)
    password = Column(String(80))
    device_name = Column(String, ForeignKey("devices.name"))
    active = Column(Boolean())
    roles = relationship(
        "Roles", secondary="roles_users", backref=backref("users", lazy=True)
    )
    fs_uniquifier = Column(
        String(255),
        unique=True,
        nullable=False,
        # Line below necessary to avoid "ValueError: Constraint must have a name"
        name="unique_fs_uniquifier_constraint",
    )

    devices = relationship("Devices", backref=backref("users", lazy=True))

    def versions(self):
        if self.devices:
            return ", ".join([release.version for device in self.devices for release in device.releases])
        else:
            return ""

    def __repr__(self):
        return self.username


class Roles(db.Model, RoleMixin):
    ...


class Devices(db.Model):
    __tablename__ = "devices"
    device_id = Column(Integer, primary_key=True)
    name = Column(String(20), unique=True)
    country = Column(String(3), nullable=True)

    releases = relationship("Releases", backref=backref("devices", lazy=True))

    def __repr__(self):
        return f"{self.name.capitalize()}, country: ({self.country})"


class Releases(db.Model):
    __tablename__ = "releases"
    release_id = Column(Integer, primary_key=True)
    device_id = Column(Integer, ForeignKey("devices.device_id"))
    version = Column(String(20))  # e.g. 8.0.122
    flag_visible = Column(Boolean())

    def __repr__(self):
        return f"{self.version}"

Then I have coded the visualization of the list of Users for Flas_admin:

class UserAdminView(ModelView):
    # Actual columns' title as seen in the website
    column_list = ("username", "versions", "active", "roles")
    # Link the columns' title and the model class attribute, so to make data sortable
    column_sortable_list = (
        "username",
        ("versions", "device_name"),
        "active",
        ("roles", "roles.name"),
    )

    def is_accessible(self):
        return (
            current_user.is_active
            and current_user.is_authenticated
            and any(role.name == "administrator" for role in current_user.roles)
        )

    def _handle_view(self, name):
        if not self.is_accessible():
            return redirect(url_for("security.login"))

    @staticmethod
    def _display_roles(view, context, model, name):
        return ", ".join([role.name.capitalize() for role in model.roles])
    
    @staticmethod
    def _display_versions(view, context, model, name):
        return model.versions()

    column_formatters = {"roles": _display_roles, "versions": _display_versions}

admin.add_view(UserAdminView(Users, db.session))

However, I get this (double) error:

Traceback (most recent call last):
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/base.py", line 369, in _run_view
    return fn(self, *args, **kwargs)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/model/base.py", line 2029, in index_view
    return self.render(
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/base.py", line 308, in render
    return render_template(template, **kwargs)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/templating.py", line 152, in render_template
    return _render(app, template, context)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/templating.py", line 133, in _render
    rv = template.render(context)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/jinja2/environment.py", line 1301, in render
    self.environment.handle_exception()
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/jinja2/environment.py", line 936, in handle_exception
    raise rewrite_traceback_stack(source=source)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/templates/bootstrap3/admin/model/list.html", line 6, in top-level template code
    {% import 'admin/model/row_actions.html' as row_actions with context %}
  File "/home/arpaia/customer-webpage-rewrite/app/templates/admin/master.html", line 1, in top-level template code
    {% extends 'admin/base.html' %}
  File "/home/arpaia/customer-webpage-rewrite/app/templates/admin/base.html", line 38, in top-level template code
    {% block page_body %}
  File "/home/arpaia/customer-webpage-rewrite/app/templates/admin/base.html", line 78, in block 'page_body'
    {% block body %}{% endblock %}
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/templates/bootstrap3/admin/model/list.html", line 68, in block 'body'
    {% block model_list_table %}
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/templates/bootstrap3/admin/model/list.html", line 116, in block 'model_list_table'
    {% block list_row scoped %}
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/templates/bootstrap3/admin/model/list.html", line 146, in block 'list_row'
    {{ get_value(row, c) }}
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/model/base.py", line 1877, in get_list_value
    return self._get_list_value(
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/model/base.py", line 1836, in _get_list_value
    value = column_fmt(self, context, model, name)
  File "/home/arpaia/customer-webpage-rewrite/app/__init__.py", line 118, in _display_versions
    return model.versions()
  File "/home/arpaia/customer-webpage-rewrite/app/models.py", line 37, in versions
    return ", ".join([release.version for device in self.devices for release in device.releases])
TypeError: 'Devices' object is not iterable

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/app.py", line 1478, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/app.py", line 1458, in wsgi_app
    response = self.handle_exception(e)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/app.py", line 1455, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/app.py", line 869, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/app.py", line 867, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask/app.py", line 852, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/base.py", line 69, in inner
    return self._run_view(f, *args, **kwargs)
  File "/home/arpaia/customer-webpage-rewrite/.venv/lib/python3.10/site-packages/flask_admin/base.py", line 371, in _run_view
    return fn(cls=self, **kwargs)
TypeError: BaseModelView.index_view() got an unexpected keyword argument 'cls'

Can someone help me, please?

I was expecting to see an empty field on the front-end or at least None, due to the following code in my Users model:

def versions(self):
        if self.devices:
            return ", ".join([release.version for device in self.devices for release in device.releases])
        else:
            return ""

Answer 1

Your database models should have __str__ methods, Flask-Admin will use this to display model instances in the UI.

Your formatters should be regular method instances and not static methods. e.g.

def _display_roles(view, context, model, name):
    return ", ".join([role.name.capitalize() for role in model.roles])

Here, the view parameter is the view instance, normally written as self.

Answer 2

@Jonathan!

Thank you for your help! I have found the issue and that was the origin of both bugs.

Basically, I was iterating through the wrong object(s): I needed to retrieve all the release versions linked to a particular device from the table Devices. Here below, there is the correct version of the code.

def versions(self):
    if self.devices:
        return ", ".join(release.version for release in self.devices.releases)
    else:
        return ""