Re: order_by clause to preserve order in list? - redux

2011-02-21 Thread Phlip 
>   SELECT * FROM table WHERE id IN (1, 3, 2) ORDER BY
>        FIELD( id, 1, 3, 2 )

I got it to work, but I had to borrow .extra(where=[]), which I
consider a spectacular design failure of the .extra(order_by=[])
system.

Firstly, I TDD using SQLite3, so I had to write code to build either
FIELD( id, 1, 3, 2 ) for MySQL, or (CASE id WHEN 1 THEN 0 WHEN 3 THEN
1 WHEN 2 THEN 2 END) for SQLite3.

Then I attack the query builder like this:

  items = items.extra(where=['1=1) ORDER BY (' + order_by_string])

I don't understand why .extra(order_by) has the same "conveniences" as
the .order_by() builder. It insisted on parsing my string instead of
simply appending it.

> --
>   Phlip
>  http://zeekland.zeroplayer.com/

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order_by clause to preserve order in list? - redux

2011-02-21 Thread Phlip 
Djangoes:

I have this question, copied from the archives:

8<-

I want to fetch a list of items in my database, and I have their id
ready:

   my_ids_to_get = [ 1, 3, 2, ]

In mysql I would fetch them like this:

  SELECT * FROM table WHERE id IN (1, 3, 2) ORDER BY
   FIELD( id, 1, 3, 2 )

This would preserve their order.

Can I build this query with the native django order_by?

I can get the objects like this:

  MyObject.objects.filter(pk__in=my_ids_to_get)

But I'm not able to build an order clause to use with it, and their
order is not preserved.

Do I have to fall back on raw sql to do this?

8<-

The answer in the archives is untenable (it's "go euphemism
yourself!"), so I'm wondering if anything has improved since the Stone
Age, 2008.

  
http://groups.google.com/group/django-users/browse_thread/thread/f23b2bdf24ff7a26/110d3e5c9e69ca63

I will, of course, start with extra(), and see where that takes me!

--
  Phlip
  http://zeekland.zeroplayer.com/

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