Save the related objects before the actual object being edited on django admin

Question

Is it possible to save the related objects before the actual object being edited on a django admin form?

For example:

in models.py

class Parent(model.Model):
    pass

class Child(model.Model):
    parent = models.ForeignKey(Parent)

@receiver(post_save,sender = Parent)
def notify_parent_save(sender, instance=None, **kwargs):
    print "Parent save"

@receiver(post_save,sender = Child)
def notify_child_save(sender, instance=None, **kwargs):
    print "Child saved"

in admin.py

class ChildInline(admin.TabularInline):
    model = Child
    extra = 1

class ParentsAdmin(admin.ModelAdmin):
    inlines = [ChildInline]

admin.site.register(Parent,ParentsAdmin)

Now, in django admin if I save a parent object, it will output on the console.

Parent save
Child save

I need this to happen in revese order:

Child save
Parent save

Answer 1

The following will save the children first:

class ParentAdmin(admin.ModelAdmin):
    inlines = [ChildInline]

    def save_model(self, request, obj, form, change):
        pass # don't actually save the parent instance

    def save_formset(self, request, form, formset, change):
        formset.save() # this will save the children
        form.instance.save() # form.instance is the parent

Answer 2

I was having issues with the answers in this post, so I figured out a more concise answer. I was having an issue because using django-fsm, the other answers here would try to save the model multiple times (once for every formset) rather than once at the end.

def save_model(self, request, obj, form, change):
    if not obj.pk: # call super method if object has no primary key 
        super(YourAdmin, self).save_model(request, obj, form, change)
    else:
        pass # don't actually save the parent instance

def save_related(self, request, form, formsets, change):
    form.save_m2m()
    for formset in formsets:
        self.save_formset(request, form, formset, change=change)
    super(YourAdmin, self).save_model(request, form.instance, form, change)

This essential just flips the order of save_model and save_related as called in Django ModelAdmin source