[1.7.x] Fixed #22349 -- Added a note clarifying `RawQuerySet` has no `__len__`.
Thanks cdestigter for the report.
Backport of 2d425116e2
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@ -419,6 +419,7 @@ answer newbie questions, and generally made Django that much better:
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Javier Mansilla <javimansilla@gmail.com>
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masonsimon+django@gmail.com
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Manuzhai
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Moayad Mardini <moayad.m@gmail.com>
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Petr Marhoun <petr.marhoun@gmail.com>
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Petar Marić <http://www.petarmaric.com/>
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Nuno Mariz <nmariz@gmail.com>
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@ -33,7 +33,8 @@ return model instances:
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This method takes a raw SQL query, executes it, and returns a
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``django.db.models.query.RawQuerySet`` instance. This ``RawQuerySet`` instance
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can be iterated over just like a normal QuerySet to provide object instances.
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can be iterated over just like a normal
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:class:`~django.db.models.query.QuerySet` to provide object instances.
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This is best illustrated with an example. Suppose you have the following model::
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@ -84,6 +85,17 @@ options that make it very powerful.
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both rows will match. To prevent this, perform the correct typecasting
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before using the value in a query.
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.. warning::
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While a ``RawQuerySet`` instance can be iterated over like a normal
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:class:`~django.db.models.query.QuerySet`, ``RawQuerySet`` doesn't
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implement all methods you can use with ``QuerySet``. For example,
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``__bool__()`` and ``__len__()`` are not defined in ``RawQuerySet``, and
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thus all ``RawQuerySet`` instances are considered ``True``. The reason
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these methods are not implemented in ``RawQuerySet`` is that implementing
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them without internal caching would be a performance drawback and adding
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such caching would be backward incompatible.
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Mapping query fields to model fields
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------------------------------------
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