Django - modèles d'administration ne reconnaissent pas les champs hérités - Stack Overflow

I get a FieldError with the following "Exception Value: Unknown field(s) (creation_date) specified for Module. Check fields/fieldsets/exclude attributes of class ModuleAdmin" if I use the admin interface to get the following model "Module":

class GeneralModel(models.Model):
    creation_date = models.DateTimeField('date of creation', auto_now_add=True)
    edited_date = models.DateTimeField('date of last modification', auto_now=True)

    class Meta:
        abstract = True


class Module(GeneralModel):
    name = models.CharField(max_length=100)
    shortDescription = models.CharField("summary", max_length=100)
    description = models.CharField("description", max_length=1500)
    authors = models.ManyToManyField("Author", through="Authorship")

    def __unicode__(self):
        return self.name

With the following ModelAdmin Code:

class ModuleAdmin(admin.ModelAdmin):
    def formfield_for_dbfield(self, db_field, **kwargs):
        formfield = super(ModuleAdmin, self).formfield_for_dbfield(db_field, **kwargs)
        if db_field.name == 'description':
            formfield.widget = forms.Textarea(attrs=formfield.widget.attrs)
        return formfield
    fieldsets = [
        ("General", {"fields": ["name", "shortDescription"]}),
        ("Details", {"fields": ["description", "creation_date"], "classes": ["collapse"]})
    ]

I get a FieldError with the following "Exception Value: Unknown field(s) (creation_date) specified for Module. Check fields/fieldsets/exclude attributes of class ModuleAdmin" if I use the admin interface to get the following model "Module":

class GeneralModel(models.Model):
    creation_date = models.DateTimeField('date of creation', auto_now_add=True)
    edited_date = models.DateTimeField('date of last modification', auto_now=True)

    class Meta:
        abstract = True


class Module(GeneralModel):
    name = models.CharField(max_length=100)
    shortDescription = models.CharField("summary", max_length=100)
    description = models.CharField("description", max_length=1500)
    authors = models.ManyToManyField("Author", through="Authorship")

    def __unicode__(self):
        return self.name

With the following ModelAdmin Code:

class ModuleAdmin(admin.ModelAdmin):
    def formfield_for_dbfield(self, db_field, **kwargs):
        formfield = super(ModuleAdmin, self).formfield_for_dbfield(db_field, **kwargs)
        if db_field.name == 'description':
            formfield.widget = forms.Textarea(attrs=formfield.widget.attrs)
        return formfield
    fieldsets = [
        ("General", {"fields": ["name", "shortDescription"]}),
        ("Details", {"fields": ["description", "creation_date"], "classes": ["collapse"]})
    ]

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