Proposal: Ordering in the admin and via the model API

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Jonas Pfeil

Nov 12, 2008, 6:58:07 PM11/12/08
to Django developers
The idea of an ordered many-to-many field is very old [1] and has been
proposed a lot over the years (e.g. [2], [3]). So the general
consensus seems to be that we want such a thing. I’d like to share
some thoughts on how to approach the whole ordering problem on the API
side (leaving aside the JavaScript implementation issues for a

I can think of three things we would want an ordering UI for in the

* A yet to be devised OrderedManyToMany field
* A ManyToMany field with an intermediary model
* Ordinary models (in the change list)


We could either subclass ManyToMany or introduce another option (like
ordered=True). I think subclassing is better, because of the extra
functions we could add to manipulate the many-to-many set. Like:

* move_up/down(item) – Moves the item one slot up or down in the list
* swap(a, b) – Swaps the places of item a and b
* insert(item, position) – Puts the item at the stated position,
pushing the other items down (or we just add a position argument to add
() and create())
* push/pop() – Or just add/create() without position argument and
remove() with no arguments at all

Of course the existing functions like all(), assignment of a list to
the field and so on should all respect the order too.

Many-to-many fields with intermediary models should also return the
correct order when reading the set, even if they do not support create
(), add() and assignment of a list.

Ordinary models and ManyToMany fields with an intermediary model

These two use cases share the need to define the field which should be
used for ordering. I found it difficult to come up with a name that
can’t be confused with 'ordering' too easily. How about this:

class Membership(models.Model):
order = models.IntegerField()

class Meta:
order_control_field = ‘order’

On a side note: When the change list in the admin is ordered on
something else than the order_control_field, an ordering UI stops
making sense (see description on [4]). A solution would be to just
switch off ordering on other fields if order_control_field is set. For
inlines this problem is nonexistent as the admin currently doesn’t
reorder the inlined items when you click the column header.

Ok, these are my ideas on how ordering could work for the user. What
do people think?




Nov 12, 2008, 8:23:38 PM11/12/08
to Django developers
I'd just like to point out that this isn't something to solve just for
many to many's, it's also for ForeignKeys.
> [3]
> [4]

David Cramer

Nov 12, 2008, 8:58:14 PM11/12/08
to Django developers
Ya this is much more needed for me on ForeignKey's, but that's like
adding magical models (which I like!).

You'd have to add left order, and right order fields, on the model
referenced in the ForeignKey, to have an OrderedForeignKey field.
This, without migrations, would not be fun with DB maintenance :)

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