Django CMS - Copy relations in custom plugin not working - django-cms

Question

I have a problem with copy_relations after publishing a page.
I have a plugin with additional model. This model has ForeignKey to my plugin.
class InfContactForm(CMSPlugin):
name = models.CharField(max_length=50)
def copy_relations(self, oldinstance):
self.inf_contact_form.all().delete()
for inf_contact_form in oldinstance.inf_contact_form.all():
inf_contact_form.pk = None
inf_contact_form.plugin = self
inf_contact_form.save()
class InfContactFormAgreement(models.Model):
inf_contact_form = models.ForeignKey(InfContactForm, related_name="inf_contact_form")
agreement = HTMLField(blank=True, null=True)
The "InfContactFormAgreement" model is then used as stacked inline in "InfContactForm" plugin form.
Like it is written in docs, there is also copy_relations() method but when the page is published, nothing happens. When I get back again to edit mode InfContactFormAgreement is doubled every time I do it.
Here is also my cms_plugins.py file:
class PluginInfContactForm(CMSPluginBase):
render_template = '_contact_form.html'
name = name1
model = InfContactForm
require_parent = False
inlines = [AgreementStackedInline, ]
def render(self, context, instance, placeholder):
context['instance'] = instance
context = super(PluginInfContactForm, self).render(context, instance, placeholder)
agreements = instance.inf_contact_form.all()
context.update({
'agreements': agreements,
})
return context
plugin_pool.register_plugin(PluginInfContactForm)
Thank you for any advice.

Answer 1

instead of:
inf_contact_form.plugin = self
you should use:
inf_contact_form.inf_contact_form = self
and the resulting code should look like this:
def copy_relations(self, oldinstance):
self.inf_contact_form.all().delete()
for inf_contact_form in oldinstance.inf_contact_form.all():
inf_contact_form.pk = None
inf_contact_form.inf_contact_form = self
inf_contact_form.save()
regards

Answer 2

I had a similar situation, the only difference being that my many-to-many relationship was not in a plugin, but an extension (PageExtension).
In my case, #Dariusz solution did not work, and I had to update the implicit "inbetween" model that exists between the Extension model and the Associated model.
My solution (the key being the "through"):
class Extension(PageExtension):
tags_regions = models.ManyToManyField(Region, related_name="articles", blank=True)
def copy_relations(self, oldinstance):
for region_tag in oldinstance.tags_regions.through.objects.filter(extension=oldinstance):
region_tag.extension = self
region_tag.save()