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Updated documentation about dereferencing

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Refs #206
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Ross Lawley 2011-06-27 12:42:26 +01:00
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commit b039a2293f
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docs/changelog.rst
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@ -5,6 +5,7 @@ Changelog
Changes in dev Changes in dev
============== ==============
- Added select_related() support
- Added support for the positional operator - Added support for the positional operator
- Updated geo index checking to be recursive and check in embedded documents - Updated geo index checking to be recursive and check in embedded documents
- Updated default collection naming convention - Updated default collection naming convention

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docs/guide/querying.rst
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@ -175,6 +175,22 @@ to be created::
>>> a.name == b.name and a.age == b.age >>> a.name == b.name and a.age == b.age
True True
Dereferencing results
---------------------
When iterating the results of :class:`~mongoengine.ListField` or
:class:`~mongoengine.DictField` we automatically dereference any
:class:`~pymongo.dbref.DBRef` objects as efficiently as possible, reducing the
number the queries to mongo.
There are times when that efficiency is not enough, documents that have
:class:`~mongoengine.ReferenceField` objects or
:class:`~mongoengine.GenericReferenceField` objects at the top level are
expensive as the number of queries to MongoDB can quickly rise.
To limit the number of queries use
:func:`~mongoengine.queryset.QuerySet.select_related` which converts the
QuerySet to a list and dereferences as efficiently as possible.
Default Document queries Default Document queries
======================== ========================
By default, the objects :attr:`~mongoengine.Document.objects` attribute on a By default, the objects :attr:`~mongoengine.Document.objects` attribute on a