title: Using Djongo's ArrayField at Django Admin
body: <p><a href="https://www.djongomapper.com/" rel="nofollow noreferrer">Djongo</a> is a <em>Django and MongoDB database connector</em> witch brings, beside others, the <a href="https://github.com/nesdis/djongo/blob/1881e96f4845eb515addcc52eb3e80e70ad23de9/djongo/models/fields.py#L301" rel="nofollow noreferrer">ArrayField</a> to Django Models. It allows one to store multiple instances of an other <code>djongo.models.Model</code> in an unique <a href="https://docs.mongodb.com/manual/tutorial/query-arrays/" rel="nofollow noreferrer">MongoDB Array field</a> inside a document related with the <code>Model</code> that has the <code>Arrayfield</code></p>
  <p>As described in source documentation:
  &quot;The model of the container must be declared as abstract, thus should not be treated as a collection of its own.&quot;</p>
  <p>As well as in <a href="https://www.djongomapper.com/using-django-with-mongodb-array-field/#using-arrayfield-in-django-admin" rel="nofollow noreferrer">djongo's site tutorials</a>
  &quot;In case you don’t plan on using your embedded model as a standalone model (which means it will always be embedded inside a parent model) you should add the <code>class Meta</code> and <code>abstract = True</code> This way Djongo will never register this model as an actual model.&quot;</p>
  <p>This way I made:</p>
  <pre class="lang-py prettyprint-override"><code># models.py
  
  class Contact(models.Model):
      key = models.CharField(max_length=100)
  
      class Meta:
          abstract = True
  
  class ContactForm(forms.ModelForm):
      class Meta:
          model = Contact
          fields = ('key',)
  
  class Person(models.Model):
      _id = models.ObjectIdField()
      ...
      contact = models.ArrayField(
          model_container=Contact,
          model_form_class=ContactForm,
      )
  
      objects = models.DjongoManager()
  </code></pre>
  <pre class="lang-py prettyprint-override"><code># admin.py
  
  admin.site.register(Person)
  </code></pre>
  <pre class="lang-sh prettyprint-override"><code>$ pip freeze
  Django==3.2.4
  djongo==1.3.6
  pymongo==3.11.4
  ...
  </code></pre>
  <p>However when I try to add a <code>Person</code> through Django Admin (in /admin/&lt;app&gt;/person/add/) I receive the error <strong>Abstract models cannot be instantiated</strong> from <code>.../django/db/models/base.py</code></p>
  <p>This seems inconsistent with Djongo's description. Am I doing something wrong?</p>