ManyToManyRel without through

Hi, I'm a beginner in Django.

I try implement both sides acces to m2m relation and I have found this old article about it:

https://www.lasolution.be/blog/related-manytomanyfield-django-admin-site.html

Starting question:

1) is this still the good way in 2017/dj2.0? do we have something better for this goal?

If no, then it almost works for me,

but I cannot add the wrapper for [+] (for adding of new records) - that has been described in the end of the article.

I have this code:

class PersonForm(forms.ModelForm):
    ...
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        if self.instance.pk:
            # if this is not a new object, we load related teams
            self.initial['teams'] = self.instance.team_set.values_list('pk', flat=True)
            rel = ManyToManyRel(self, Team)
            self.fields['teams'].widget = RelatedFieldWidgetWrapper(self.fields['teams'].widget, rel, admin.site)

The last 2 lines should add the wrapper, but there is a problem.

I use a ManyToManyField without through=..

ManyToManyRel() creates the object (with default parameter through=None), however it fails while creating RelatedFieldWidgetWrapper with error

   'NoneType' object has no attribute '_meta'

in django 2.0 code django/db/models/fields/reverse_related.py, ManyToManyRel class:

   def get_related_field(self):
          opts = self.through._meta ...

where self.through is None.

So my main question:

2) Is this issue of the ManyToManyRel class, which allows the default parameter through=None, however fails in its get_related_field() when the default is used,

or, should I change my code...?

Best regards,

Mirek

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