Annotate QuerySet with first value of ordered related model
Perhaps using .raw
isn't such a bad idea. Checking the code for Window
class we can see that essentially composes an SQL query to achieve the "Windowing".
An easy way out may be the usage of the architect module which can add partition functionality for PostgreSQL according to the documentation.
Another module that claims to inject Window functionality to Django < 2.0 is the django-query-builder which adds a partition_by()
queryset method and can be used with order_by
:
query = Query().from_table( Order, ['*', RowNumberField( 'revenue', over=QueryWindow().order_by('margin') .partition_by('account_id') ) ])query.get_sql()# SELECT tests_order.*, ROW_NUMBER() OVER (PARTITION BY account_id ORDER BY margin ASC) AS revenue_row_number# FROM tests_order
Finally, you can always copy the Window
class source code in your project or use this alternate Window class code.
Your apparent problem is that Django 1.10 is too old to handle window functions properly (which have been around for a very long time already).
That problem goes away if you rewrite your query without window function.
3 equivalent queries
Which of them is fastest depends on available indexes and data distribution. But each of them should be faster than your original.
1. With DISTINCT ON
:
SELECT DISTINCT ON (p.id) p.id, b.titleFROM blog_post pLEFT JOIN book b ON b.author_id = p.author_id AND b.genre = 'mystery' AND b.date_published >= p.date_publishedORDER BY p.id, b.date_published;
Related, with detailed explanation:
2. With a LATERAL
subquery (requires Postgres 9.3 or later):
SELECT p.id, b.titleFROM blog_post pLEFT JOIN LATERAL ( SELECT title FROM book WHERE author_id = p.author_id AND genre = 'mystery' AND date_published >= p.date_published ORDER BY date_published LIMIT 1 ) b ON true;-- ORDER BY p.id -- optional
Related, with detailed explanation:
3. Or simpler, yet, with a correlated subquery:
SELECT p.id ,(SELECT title FROM book WHERE author_id = p.author_id AND genre = 'mystery' AND date_published >= p.date_published ORDER BY date_published LIMIT 1)FROM blog_post p;-- ORDER BY p.id -- optional
Each should be translated easily to Django syntax. You might also just use the raw SQL, that's what is sent to the Postgres server anyway.