StackOverflow2013

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10698721
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2012-05-22T08:52:53.183
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2012-05-22T09:00:53.943
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Body
If you are using PostgreSQL as a database backend and don't need cross database compatibility, you can use the <a href="http://www.postgresql.org/docs/9.1/static/functions-window.html" rel="nofollow">powerful window functions</a> that allow something like that : Imagine your table looks like that : <pre><code>CREATE TABLE x ( i serial primary key, value integer not null, date timestamp, category text); </code></pre> And you want the most recent value for each category. You will do : <pre><code>SELECT first_value(i) over w, first_value(value) over w, first_value(date) over w category, FROM x WINDOW w AS (PARTITION BY category ORDER BY date DESC); </code></pre> You can use such a query in django via the <code>raw</code> method on the query set manager : <pre><code>ModelX.objects.raw("""SELECT DISTINCT ....... FROM x WINDOW w .....""") </code></pre> To get the last N entries by category, the query is a little more complicated and involves a subquery : <pre><code>SELECT i, value, date, category FROM (SELECT i, value, date, category, row_number() over w FROM x WINDOW w AS (PARTITION BY category ORDER BY date DESC)) AS subquery WHERE subquery.row_number <= 30; </code></pre> Seeing that, you could even make a view : <pre><code>CREATE VIEW x_with_reverse_date_index AS (SELECT i, value, date, category, row_number() over w FROM x WINDOW w AS (PARTITION BY category ORDER BY date DESC)); </code></pre> And create a django model that queries this view : <pre><code>class ModelX(models.Model): ... ... row_number = models.IntegerField("Row number when ordering by date desc") class Meta: db_table = 'x_with_reverse_date_index' </code></pre> and query it "normally" : <pre><code>ModelX.objects.filter(category__in = ('catA','catB'), row_number__lte = 30) ModelX.objects.filter(row_number = 29) ... </code></pre> Warning : again, don't do this if you need a code that works on another database engine.
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1. POLimit queryset results based on model field, are there better ways?
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Guidance

A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.