Re: Basic GenericForeignKey Question

Hey Ludovic,

I simplified things a lot to illustrate my particular issue, but our permission system is actually pretty complex - the permissions can apply to any individual object, and they are also hierarchical like those that would apply to a folder system. I found there were decent extensions to the Django permission system to handle object-level permissions, and hierarchical permissions, but not both.

On Wednesday, September 21, 2016 at 9:11:44 AM UTC-6, ludovic coues wrote:

Unrelated, do you have any reason to not reuse the existing django
permission system ?

2016-09-21 16:41 GMT+02:00 TheBeardedTemplar <thebeard...@gmail.com>:
> Hey all,
>
> I'm just getting started with GenericForeignKeys and I've run into a small
> point of confusion. I'm implementing a very general permission system as
> follows:
>
> class Permission(models.Model):
>     """
>     This stores permissions for a single object.
>     """
>     #These 3 fields are used to implement a generic foreign key
>     content_type = models.ForeignKey(ContentType)
>     object_id = models.PositiveIntegerField()
>     model = GenericForeignKey()
>
>     user = models.ForeignKey(User)
>
>     #Permissions
>     read = models.BooleanField(default=False)
>     write = models.BooleanField(default=False)
>     delete = models.BooleanField(default=False)
>
>
>
> I also have a check permission function as follows:
>     def checkPermission(self, obj, user, action):
>         try:
>             p = Permission.objects.get(model=obj, user=user)
>             return getattr(p, action)
>         except ObjectPermission.DoesNotExist:
>             return False
>
> Currently this fails because I'm trying to access the GenericForeignKey
> directly, and I get this error:
> django.core.exceptions.FieldError: Field 'model' does not generate an
> automatic reverse relation and therefore cannot be used for reverse
> querying. If it is a GenericForeignKey, consider adding a GenericRelation.
>
> I've spent a while reading about GenericRelations but I'm still not exactly
> sure how to go about this. The Django documentation shows using
> GenericRelation fields on the models that my Permission points to, but it
> can point to many many different things and I'm hoping to get a way to use
> this functionality without putting a GenericRelation on every possible
> linked to model.
>
> Thanks!
>
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--

Cordialement, Coues Ludovic
+336 148 743 42

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