FlatPage model field url is not unique

[jesper@…]

You can create several pages with the same URL, which makes the middleware barf.

I'm not submitting a patch, but I'd imagine it to be as easy as adding an index on (url, site_id).

[arien <regexbot@…>]

trivial patch to ensure url is unique

[Jesper Noehr <jesper@…>]

Arien,

I don't think it's an appropriate fix to set unique=True on url alone. Flatpages are per site, and sites can have the same urls. I think the unique constraint needs to be on (url, site_id) as I mentioned in my initial report.

[arien <regexbot@…>]

Right you are; I can't believe I missed that both in your description and the docs...!

I don't think this can be fixed in a meaningful way without changing the many-to-many relationship between FlatPages and Sites. For example, what should happen if you create an /about/ page and decide to use it on more than one site, and then later you add create another /about/ page for one of these same sites (and possibly others)?

[Jesper Noehr <jesper@…>]

Hm, you have a good point. Although--without knowing the inner workings on ManyToMany--I do believe that if the unique constraint lives on (url, site_id), then you *can* use it cross-site. E.g.

('/about/', 1) and ('/about/', 2) would be fine with that constraint. However, you cannot create a new ('/about', 2) anymore, since the contraint won't allow you to. Please correct me if I'm wrong :-)

[arien <regexbot@…>]

You cannot have a unique constraint across tables.

You could prevent creating duplicates by checking what combinations are "taken" before saving: you raise an exception if the FlatPage you're about to save has one or more Sites that are already used by another FlatPage (i.e. one with a different id) with the same URL (path, really). But you'd have to do that in a transaction, and since not all databases used with Django are guaranteed to have those...

Changing ​the view to use get_list_or_404 (and picking one of the results) instead of get_object_or_404 isn't really an option either, so I think punting was probably the right decision.

[Jesper Noehr <jesper@…>]

I don't entirely agree with that. The constraint is not across tables, as I'm not suggesting (url, site) but (url, site_ID). Both columns are in the same table, so it's a simple unique constraint.

[James Bennett]

Replying to Jesper Noehr <jesper@noehr.org>:

I don't entirely agree with that. The constraint is not across tables, as I'm not suggesting (url, site) but (url, site_ID). Both columns are in the same table, so it's a simple unique constraint.

No, they are not in the same table; the url column is in the flatpages table, and the site_id column is in a separate join table used to implement the many-to-many relationship. Go look at your database if you don't believe me.

[anonymous]

I believe you, thank you for clarifying. As I wrote earlier, I don't know how manytomany relationships work in Django, but of course they would be linked through a link-table, now that you mention it.

I'm not really sure what to do about the constraint then.

[arien <regexbot@…>]

This is a duplicate of #702.