Flask: model_form: AttributeError: type object 'Form' has no attribute 'query'

This is the error:

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/app.py",
   line 1701, in __call__ return self.wsgi_app(environ, start_response)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/app.py",
   line 1689, in wsgi_app response =self.make_response(self.handle_exception(e))

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/app.py",
   line 1687, in wsgi_app response = self.full_dispatch_request()

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/app.py",
   line 1360, in full_dispatch_request rv = self.handle_user_exception(e)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/app.py",
   line 1358, in full_dispatch_request rv = self.dispatch_request()

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/app.py",
   line 1344, in dispatch_request return
   self.view_functions[rule.endpoint](**req.view_args)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/views.py",
   line 83, in view return self.dispatch_request(*args, **kwargs)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/views.py",
   line 150, in dispatch_request return meth(*args, **kwargs)

File"/www/sites/MyBlog/app/posts.py", line 38, in get return
   render_template('posts/detail.html', **context)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/templating.py",
   line 125, in render_template context, ctx.app)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/flask/templating.py",
   line 107, in _render rv = template.render(context)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/jinja2/environment.py",
   line 894, in render return
   self.environment.handle_exception(exc_info, True)

File"/www/sites/MyBlog/app/templates/posts/detail.html", line 9, in
   toplevel template code {% block content %}

File"/www/sites/MyBlog/app/templates/posts/detail.html", line 23, in
   block "content" {{ forms.render(form) }}

File"/www/sites/MyBlog/app/templates/_forms.html", line 13, in template
   {{ field() }} 

File"/www/sites/blog/flask/lib/python2.7/sitepackages/wtforms/fields/core.py",
   line 140, in __call__ return self.widget(self, **kwargs)

File"/www/sites/blog/flask/lib/python2.7/sitepackages/wtforms/widgets/core.py",
   line 246, in __call__ for val, label, selected in field.iter_choices():

File"/www/sites/blog/flask/lib/python2.7/sitepackages/wtforms/ext/sqlalchemy/fields.py",
   line 108, in iter_choices for pk, obj in self._get_object_list():

File"/www/sites/blog/flask/lib/python2.7/sitepackages/wtforms/ext/sqlalchemy/fields.py",
   line 99, in _get_object_list Display the sourcecode for this
   frameOpen an interactive python shell in this framequery = self.query
   or self.query_factory()

File"/www/sites/blog/flask/lib/python2.7/sitepackages/wtforms/ext/sqlalchemy/orm.py",
   line 117, in <lambda> 'query_factory': lambda:
   db_session.query(foreign_model).all() AttributeError: type object
   'Form' has no attribute 'query'

This is my view.py method

class DetailView(MethodView):

  def get_context(self, slug):

    p = Post('','',slug)
    post = p.get_or_404(slug)

    form = model_form(Comment, Form, exclude=['timestamp'])(request.form)
    context = {
      "post": post,
      "form": form
    }
    return context

  def get(self, slug):
    context = self.get_context(slug)
    return render_template('posts/detail.html', **context)

  def post(self, slug):
    context = self.get_context(slug)
    form = context.get('form')

    if form.validate_on_submit():
      comment = Comment()
      form.populate_obj(comment)

      post = context.get('post')
      post.comments.append(comment)
      db.session.commit()

      return redirect(url_for('posts.detail', slug=slug))

    return render_template('posts/detail.html', **context)

and this is my template for form:

{% macro render(form) %}
<fieldset>
{% for field in form %}
{% if field.type in ['CSRFTokenField', 'HiddenField'] %}
  {{ field() }}
{% else %}
  <div class="clearfix {% if field.errors %}error{% endif %}">
    {{ field.label }}
    <div class="input">
      {% if field.name == "body" %}
        {{ field(rows=10, cols=40) }}
      {% else %}
        {{ field() }}
      {% endif %}
      {% if field.errors or field.help_text %}
        <span class="help-inline">
        {% if field.errors %}
          {{ field.errors|join(' ') }}
        {% else %}
          {{ field.help_text }}
        {% endif %}
        </span>
      {% endif %}
    </div>
  </div>
{% endif %}
{% endfor %}
</fieldset>
{% endmacro %}

I am getting an error related to following code

form = model_form(Comment, Form, exclude=['timestamp'])(request.form)

and:

{{ field() }}

please suggest some solution. Thanks in advance.