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18-May-2020 05:19

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The above example will return the last item first, then the penultimate item and so on. If you order by fields from a related model, those fields will be added to the selected columns and they may make otherwise duplicate rows appear to be distinct.Since the extra columns don’t appear in the returned results (they are only there to support ordering), it sometimes looks like non-distinct results are being returned.Each foreign key you add will implicitly include all of its default orderings as well.If a query doesn’t have an ordering specified, results are returned from the database in an unspecified order.It’s more efficient to select only the fields you need to use.Finally, note that you can call attributes and reverse relations can have multiple related rows, including these can have a multiplier effect on the size of your result set.Only aggregate expressions that reference a single field can be anonymous arguments. For example, if you were manipulating a list of blogs, you may want to determine how many entries have been made in each blog: queries may be expensive and slow, depending on the database backend you’re using.

The aggregation functions that are provided by Django are described in Aggregation Functions below.If you generate a pickle using Django version N, there is no guarantee that pickle will be readable with Django version N 1.Pickles should not be used as part of a long-term archival strategy.A particular ordering is guaranteed only when ordering by a set of fields that uniquely identify each object in the results.

For example, if a Note that this is not quite the same as slicing from the end of a sequence in Python.Similarly, if you use a that returns dictionaries, rather than model instances, when used as an iterable.