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17 changes: 14 additions & 3 deletions snooty.toml
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Expand Up @@ -9,8 +9,15 @@ intersphinx = [

toc_landing_pages = [
"/installation",
"/api-abi-versioning"
]
"/api-abi-versioning",
"/get-started",
"/connect",
"/read",
"/write",
"/indexes",
"/security",
"/data-formats",
]

sharedinclude_root = "https://raw.githubusercontent.com/10gen/docs-shared/main/"

Expand All @@ -20,4 +27,8 @@ driver-long = "MongoDB C++ Driver"
driver-short = "C++ driver"
version = "3.10"
full-version = "{+version+}.2"
api = "https://mongocxx.org/api/current"
api = "https://mongocxx.org/api/current"
string-data-type = "``string``"
int-data-type = "``int``"
stable-api = "Stable API"
mdb-server = "MongoDB Server"
195 changes: 195 additions & 0 deletions source/aggregation.txt
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.. _cpp-aggregation:

====================================
Transform Your Data with Aggregation
====================================

.. facet::
:name: genre
:values: reference

.. meta::
:keywords: code example, transform, computed, pipeline
:description: Learn how to use the C++ driver to perform aggregation operations.

.. contents:: On this page
:local:
:backlinks: none
:depth: 2
:class: singlecol

.. TODO:
.. toctree::
:titlesonly:
:maxdepth: 1

/aggregation/aggregation-tutorials

Overview
--------

In this guide, you can learn how to use the {+driver-short+} to perform
**aggregation operations**.

Aggregation operations process data in your MongoDB collections and
return computed results. The MongoDB Aggregation framework, which is
part of the Query API, is modeled on the concept of data processing
pipelines. Documents enter a pipeline that contains one or more stages,
and this pipeline transforms the documents into an aggregated result.

An aggregation operation is similar to a car factory. A car factory has
an assembly line, which contains assembly stations with specialized
tools to do specific jobs, like drills and welders. Raw parts enter the
factory, and then the assembly line transforms and assembles them into a
finished product.

The **aggregation pipeline** is the assembly line, **aggregation stages** are the
assembly stations, and **operator expressions** are the
specialized tools.

Aggregation Versus Find Operations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can use find operations to perform the following actions:

- Select which documents to return
- Select which fields to return
- Sort the results

You can use aggregation operations to perform the following actions:

- Run find operations
- Rename fields
- Calculate fields
- Summarize data
- Group values

Limitations
~~~~~~~~~~~

Keep the following limitations in mind when using aggregation operations:

- Returned documents cannot violate the
:manual:`BSON document size limit </reference/limits/#mongodb-limit-BSON-Document-Size>`
of 16 megabytes.
- Pipeline stages have a memory limit of 100 megabytes by default. You can exceed this
limit by setting the ``allow_disk_use`` field of a ``mongocxx::options::aggregate``
instance to ``true``.

.. important:: $graphLookup Exception

The :manual:`$graphLookup
</reference/operator/aggregation/graphLookup/>` stage has a strict
memory limit of 100 megabytes and ignores the ``allow_disk_use`` field.

.. _cpp-aggregation-example:

Aggregation Example
-------------------

.. note::

The examples in this guide use the ``restaurants`` collection in the ``sample_restaurants``
database from the :atlas:`Atlas sample datasets </sample-data>`. To learn how to create a
free MongoDB Atlas cluster and load the sample datasets, see the :atlas:`Get Started with Atlas
</getting-started>` guide.

To perform an aggregation, pass a ``mongocxx::pipeline`` instance containing the aggregation
stages to the ``collection.aggregate()`` method.

The following code example produces a count of the number of bakeries in each borough
of New York. To do so, it uses an aggregation pipeline that contains the following stages:

- :manual:`$match </reference/operator/aggregation/match/>` stage to filter for documents
in which the ``cuisine`` field contains the value ``"Bakery"``

- :manual:`$group </reference/operator/aggregation/group/>` stage to group the matching
documents by the ``borough`` field, accumulating a count of documents for each distinct
value

.. io-code-block::

.. input:: /includes/aggregation.cpp
:start-after: start-match-group
:end-before: end-match-group
:language: cpp
:dedent:

.. output::

{ "_id" : "Brooklyn", "count" : 173 }
{ "_id" : "Queens", "count" : 204 }
{ "_id" : "Bronx", "count" : 71 }
{ "_id" : "Staten Island", "count" : 20 }
{ "_id" : "Missing", "count" : 2 }
{ "_id" : "Manhattan", "count" : 221 }

Explain an Aggregation
~~~~~~~~~~~~~~~~~~~~~~

To view information about how MongoDB executes your operation, you can
instruct the MongoDB query planner to **explain** it. When MongoDB explains
an operation, it returns **execution plans** and performance statistics.
An execution plan is a potential way MongoDB can complete an operation.
When you instruct MongoDB to explain an operation, it returns both the
plan MongoDB executed and any rejected execution plans.

To explain an aggregation operation, run the ``explain`` database command by specifying
the command in a BSON document and passing it as an argument to the ``run_command()``
method.

The following example instructs MongoDB to explain the aggregation operation from the
preceding :ref:`cpp-aggregation-example`:

.. io-code-block::

.. input:: /includes/aggregation.cpp
:start-after: start-explain
:end-before: end-explain
:language: cpp
:dedent:

.. output::

{ "explainVersion" : "2", "queryPlanner" : { "namespace" : "sample_restaurants.restaurants",
"indexFilterSet" : false, "parsedQuery" : { "cuisine" : { "$eq" : "Bakery" } }, "queryHash":
"...", "planCacheKey" : "...", "optimizedPipeline" : true, "maxIndexedOrSolutionsReached":
false, "maxIndexedAndSolutionsReached" : false, "maxScansToExplodeReached" : false,
"winningPlan" : { ... }
... }


Additional Information
----------------------

MongoDB Server Manual
~~~~~~~~~~~~~~~~~~~~~

To view a full list of expression operators, see :manual:`Aggregation
Operators. </reference/operator/aggregation/>`

To learn about assembling an aggregation pipeline and view examples, see
:manual:`Aggregation Pipeline. </core/aggregation-pipeline/>`

To learn more about creating pipeline stages, see :manual:`Aggregation
Stages. </reference/operator/aggregation-pipeline/>`

To learn more about explaining MongoDB operations, see
:manual:`Explain Output </reference/explain-results/>` and
:manual:`Query Plans. </core/query-plans/>`

.. TODO:
Aggregation Tutorials
~~~~~~~~~~~~~~~~~~~~~

.. To view step-by-step explanations of common aggregation tasks, see
.. :ref:`cpp-aggregation-tutorials-landing`.

API Documentation
~~~~~~~~~~~~~~~~~

For more information about executing aggregation operations with the {+driver-short+},
see the following API documentation:

- `aggregate() <{+api+}/classmongocxx_1_1v__noabi_1_1collection.html#a480f6d0f9986d43b1d17d6ed8876941d>`__
- `mongocxx::options::aggregate <{+api+}/classmongocxx_1_1v__noabi_1_1options_1_1aggregate.html>`__
45 changes: 45 additions & 0 deletions source/compatibility.txt
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.. _cpp-compatibility-tables:

=============
Compatibility
=============

.. contents:: On this page
:local:
:backlinks: none
:depth: 2
:class: singlecol

.. facet::
:name: genre
:values: reference

.. meta::
:keywords: backwards compatibility, versions, upgrade

MongoDB Compatibility
---------------------

The following compatibility table specifies the recommended version or versions
of the {+driver-long+} for use with a specific version of MongoDB.

The first column lists the driver version.

.. sharedinclude:: dbx/lifecycle-schedule-callout.rst

.. sharedinclude:: dbx/compatibility-table-legend.rst

.. include:: /includes/mongodb-compatibility-table-cxx.rst

Language Compatibility
----------------------

The following compatibility table specifies the recommended version of the
{+driver-long+} for use with a specific version of C++.

The first column lists the driver version.

.. include:: /includes/language-compatibility-table-cxx.rst

For more information on how to read the compatibility tables, see our guide on
:ref:`MongoDB Compatibility Tables. <about-driver-compatibility>`
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