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DOCS-9120: emphasize BSON limit on distinct, propose agg alternative #3213

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Feb 1, 2018
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DOCS-9120: emphasize BSON limit on distinct, propose agg alternative #3213

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8 changes: 8 additions & 0 deletions source/includes/note-distinct-bson-limit-agg-alternative.rst
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@@ -0,0 +1,8 @@
.. note::

Results must not be larger than the maximum :ref:`BSON size
<limit-bson-document-size>`. If your results exceed the maximum
BSON size, use the aggregation pipeline to retrieve distinct
values using the :pipeline:`$group` operator, as described in
:ref:`Retrieve Distinct Values with the Aggregation Pipeline
<aggregation-group-distinct-values>`.
7 changes: 7 additions & 0 deletions source/includes/table-sql-to-mongo-select-examples.yaml
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Expand Up @@ -343,6 +343,13 @@ sql19: |
SELECT DISTINCT(status)
FROM people
mongo19: |
.. code-block:: javascript
:emphasize-lines: 1

db.people.aggregate( [ { $group : { _id : "$status" } } ] )

or, for distinct value sets that do not exceed the :ref:`BSON size limit <limit-bson-document-size>`

.. code-block:: javascript
:emphasize-lines: 1

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4 changes: 3 additions & 1 deletion source/reference/command/distinct.txt
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Expand Up @@ -36,9 +36,11 @@ Definition

.. include:: /includes/apiargs/dbcommand-distinct-field.rst

.. include:: /includes/note-distinct-bson-limit-agg-alternative.rst

MongoDB also provides the shell wrapper method
:method:`db.collection.distinct()` for the :dbcommand:`distinct`
command. Additionally, many MongoDB :term:`drivers <driver>` also
command. Additionally, many MongoDB :term:`drivers <driver>`
provide a wrapper method. Refer to the specific driver documentation.

Behavior
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5 changes: 3 additions & 2 deletions source/reference/method/db.collection.distinct.txt
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Expand Up @@ -22,8 +22,9 @@ Definition
.. include:: /includes/apiargs/method-db.collection.distinct-param.rst

The :method:`db.collection.distinct()` method provides a wrapper
around the :dbcommand:`distinct` command. Results must not be larger
than the maximum :ref:`BSON size <limit-bson-document-size>`.
around the :dbcommand:`distinct` command.

.. include:: /includes/note-distinct-bson-limit-agg-alternative.rst

.. _distinct-method-options:

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