fixing "assignment to the reverse side of a many-to-many.."

extend.py

@@ -0,0 +1,98 @@
+from django import forms
+from django.contrib import admin
+from django.core.exceptions import ImproperlyConfigured
+
+
+def registered_modeladmin(model_cls):
+    try:
+        model_admin_cls = type(admin.site._registry[model_cls])
+        model_admin_cls._model_cls = model_cls
+        return model_admin_cls
+    except KeyError:
+        raise ImproperlyConfigured(
+            "A ModelAdmin for %s needs to already be registered" % model_cls)
+
+
+def registered_form(model_cls):
+    admin_cls = registered_modeladmin(model_cls)
+    form_cls = admin_cls.form
+    form_cls._admin_cls = admin_cls
+    return form_cls
+
+
+def add_bidirectional_m2m(form_cls):
+
+    class BidirectionalM2MForm(form_cls):
+
+        def _get_bidirectional_m2m_fields(self):
+            try:
+                return super(BidirectionalM2MForm, self)._get_bidirectional_m2m_fields()
+            except AttributeError:
+                return []
+
+        def __init__(self, *args, **kwargs):
+            super(BidirectionalM2MForm, self).__init__(*args, **kwargs)
+            if self.instance.pk is not None:
+                for m2m_field, related_manager in self._get_bidirectional_m2m_fields():
+                    self.fields[m2m_field].initial = getattr(
+                        self.instance, related_manager).all()
+
+        def save(self, commit=True):
+            """
+            Saves this ``form``'s cleaned_data into model instance
+            ``self.instance``.
+
+            If commit=True, then the changes to ``instance`` will be saved to the
+            database.  If ``instance`` is a new object then it will get saved to
+            the database even if commit=False
+
+            Returns ``instance``.
+            """
+            instance = super(BidirectionalM2MForm, self).save(commit=False)
+            force_save = self.instance.pk is None
+            if force_save:
+                instance.save()
+            for m2m_field, related_manager in self._get_bidirectional_m2m_fields():
+#                setattr(self.instance, related_manager, self.cleaned_data[m2m_field])
+# ici ça plante  direct assignment to the reverse side of a many-to-many set is prohibited. Use suppliers.set() instead.
+
+#               self.instance.suppliers.set(self.cleaned_data[m2m_field]) #là ça marche mais avec suppliers en dur
+#               self.instance.related_manager.set(self.cleaned_data[m2m_field]) #et là ça plante 'Food' object has no attribute 'related_manager'
+#                j'appends que instance.__setattr__(attribute, value) est équivalent à instance.attribute = value
+#                self.instance.__set__(related_manager,self.cleaned_data[m2m_field]) # mais ça marche pas non plus 'Food' object has no attribute '__set__'
+# et finalement je copie la solution utilisée là https://gist.github.com/Wtower/0b181cc06f816e4feac14e7c0aa2e9d0
+                recordset = getattr(self.instance, m2m_field)
+                records = recordset.all()
+                # remove records that have been removed in form
+                for record in records:
+                    if record not in self.cleaned_data[m2m_field]:
+                        recordset.remove(record)
+                # add records that have been added in form
+                for record in self.cleaned_data[m2m_field]:
+                    if record not in records:
+                        recordset.add(record)
+
+            if commit:
+                if not force_save:
+                    instance.save()
+                self.save_m2m()
+            return instance
+
+    return BidirectionalM2MForm
+
+
+def extend_registered(extended_cls):
+    if issubclass(extended_cls, admin.ModelAdmin):
+        admin_cls = extended_cls
+        admin.site.unregister(admin_cls._model_cls)
+        admin.site.register(admin_cls._model_cls, admin_cls)
+        return admin_cls
+    elif issubclass(extended_cls, (forms.Form, forms.ModelForm)):
+        form_cls = extended_cls
+        admin_cls = form_cls._admin_cls
+        admin.site.unregister(admin_cls._model_cls)
+        admin_cls.form = form_cls
+        admin.site.register(admin_cls._model_cls, admin_cls)
+        return form_cls
+    else:
+        raise ValueError("Extended class needs to be a ModelAdmin or Form")