Fixed #22268 -- Documented values_list() behavior for multivalued relations.a
Thanks Sai Krishna for the initial patch.
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@ -637,6 +637,30 @@ achieve that, use ``values_list()`` followed by a ``get()`` call::
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>>> Entry.objects.values_list('headline', flat=True).get(pk=1)
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'First entry'
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``values()`` and ``values_list()`` are both intended as optimizations for a
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specific use case: retrieving a subset of data without the overhead of creating
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a model instance. This metaphor falls apart when dealing with many-to-many and
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other multivalued relations (such as the one-to-many relation of a reverse
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foreign key) because the the "one row, one object" assumption doesn't hold.
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For example, notice the behavior when querying across a
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:class:`~django.db.models.ManyToManyField`::
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>>> Author.objects.values_list('name', 'entry__headline')
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[('Noam Chomsky', 'Impressions of Gaza'),
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('George Orwell', 'Why Socialists Do Not Believe in Fun'),
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('George Orwell', 'In Defence of English Cooking'),
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('Don Quixote', None)]
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Authors with multiple entries appear multiple times and authors without any
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entries have ``None`` for the entry headline.
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Similarly, when querying a reverse foreign key, ``None`` appears for entries
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not having any author::
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>>> Entry.objects.values_list('authors')
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[('Noam Chomsky',), ('George Orwell',), (None,)]
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``dates()``
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~~~~~~~~~~~
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