How can I create a dictionary of two lists that preserves the order of the first list in the minimum number of queries?

Question

Let's say that I have a list of movie ids in a QuerySet in the following format:

movie_ids = [12,4,9,16]

Now, I want to pull the list of corresponding movies. I also want to minimize the number of queries. So I do the following:

movies = Movie.objects.filter(pk__in=movie_ids)

However, this query won't guarantee that movies will have the corresponding movie objects in the same order as they were in movie_ids, will it? Is there anyway to guarantee the order (so that each movie_id corresponds to the correct movie) so I can do something pair the two lists into a dictionary with:

id_movies = dict(zip(movie_ids, movies))

This would then be used in my template in Django.

possible duplicate of [Django QuerySet Custom Ordering by ID](http://stackoverflow.com/questions/3625641/django-queryset-custom-ordering-by-id) — Ignacio Vazquez-Abrams, Feb 15 '12 at 05:20

score 2 · Accepted Answer · answered Feb 15 '12 at 05:32

2

You can use the dict like

# Create the dict for the movies object.
id_movies = dict([(m.id, m) for m in movies])

# Get the data in order.
order_movies = [id_movies[i] for i in movie_ids]

This way you will get the object in same order which you gave.

answered Feb 15 '12 at 05:32

Nilesh

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Now we're first creating the list and from that the dict. Is there any reason to not go with `{m.id : m for m in movies}` which does the same (?) thing inline? – Voo Feb 15 '12 at 06:21

How can I create a dictionary of two lists that preserves the order of the first list in the minimum number of queries?

1 Answers1