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Improve Document.meta.shard_key docs (#2099)

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This closes #2096. Previous documentation of the shard_key meta attribute was
missing the crucial point that it really only matters if your collection is
sharded over a compound index.
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Stefan Wójcik 2019-06-20 11:25:51 +02:00 committed by GitHub
parent e8dbd12f22
commit ae0384df29
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2 changed files with 18 additions and 10 deletions
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18
docs/guide/defining-documents.rst
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@ -714,11 +714,16 @@ subsequent calls to :meth:`~mongoengine.queryset.QuerySet.order_by`. ::
Shard keys
==========
If your collection is sharded, then you need to specify the shard key as a tuple,
using the :attr:`shard_key` attribute of :attr:`~mongoengine.Document.meta`.
This ensures that the shard key is sent with the query when calling the
:meth:`~mongoengine.document.Document.save` or
:meth:`~mongoengine.document.Document.update` method on an existing
If your collection is sharded by multiple keys, then you can improve shard
routing (and thus the performance of your application) by specifying the shard
key, using the :attr:`shard_key` attribute of
:attr:`~mongoengine.Document.meta`. The shard key should be defined as a tuple.
This ensures that the full shard key is sent with the query when calling
methods such as :meth:`~mongoengine.document.Document.save`,
:meth:`~mongoengine.document.Document.update`,
:meth:`~mongoengine.document.Document.modify`, or
:meth:`~mongoengine.document.Document.delete` on an existing
:class:`~mongoengine.Document` instance::
class LogEntry(Document):
@ -728,7 +733,8 @@ This ensures that the shard key is sent with the query when calling the
data = StringField()
meta = {
'shard_key': ('machine', 'timestamp',)
'shard_key': ('machine', 'timestamp'),
'indexes': ('machine', 'timestamp'),
}
.. _document-inheritance:

10
mongoengine/document.py
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@ -544,7 +544,7 @@ class Document(six.with_metaclass(TopLevelDocumentMetaclass, BaseDocument)):
@property
def _qs(self):
"""Return the queryset to use for updating / reloading / deletions."""
"""Return the default queryset corresponding to this document."""
if not hasattr(self, '__objects'):
self.__objects = QuerySet(self, self._get_collection())
return self.__objects
@ -552,9 +552,11 @@ class Document(six.with_metaclass(TopLevelDocumentMetaclass, BaseDocument)):
@property
def _object_key(self):
"""Get the query dict that can be used to fetch this object from
the database. Most of the time it's a simple PK lookup, but in
case of a sharded collection with a compound shard key, it can
contain a more complex query.
the database.
Most of the time the dict is a simple PK lookup, but in case of
a sharded collection with a compound shard key, it can contain a more
complex query.
"""
select_dict = {'pk': self.pk}
shard_key = self.__class__._meta.get('shard_key', tuple())