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DOCSP-45176: Run a command #130
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Original file line number | Diff line number | Diff line change |
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.. _ruby-run-command: | ||
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||
====================== | ||
Run a Database Command | ||
====================== | ||
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||
.. contents:: On this page | ||
:local: | ||
:backlinks: none | ||
:depth: 2 | ||
:class: singlecol | ||
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||
.. facet:: | ||
:name: genre | ||
:values: reference | ||
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.. meta:: | ||
:keywords: administration, code example | ||
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Overview | ||
-------- | ||
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||
In this guide, you can learn how to use the {+driver-short+} to | ||
run a database command. You can use database commands to perform a | ||
variety of administrative and diagnostic tasks, such as fetching server | ||
statistics, initializing a replica set, or running an aggregation pipeline. | ||
|
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.. important:: Prefer Driver Methods to Database Commands | ||
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The driver provides wrapper methods for many database commands. | ||
If possible, we recommend using these methods instead of executing | ||
database commands. | ||
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||
To perform administrative tasks, use the :mongosh:`MongoDB Shell </>` | ||
instead of the {+driver-short+}. The shell provides helper methods | ||
that might not be available in the driver. | ||
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||
If there are no available helpers in the driver or the shell, you | ||
can use the ``db.runCommand()`` shell method or the driver's | ||
``command`` method, which is described in this guide. | ||
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Sample Data | ||
~~~~~~~~~~~ | ||
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||
The examples in this guide use the ``sample_restaurants`` | ||
database from the :atlas:`Atlas sample datasets </sample-data>`. To access this database | ||
from your {+language+} application, create a ``Mongo::Client`` object that connects to an Atlas cluster | ||
and assign the following value to your ``database`` variable: | ||
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||
.. literalinclude:: /includes/databases-collections/run-command.rb | ||
:language: scala | ||
:dedent: | ||
:start-after: start-db | ||
:end-before: end-db | ||
|
||
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. | ||
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Execute a Command | ||
----------------- | ||
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To run a database command, run the ``command`` instance method of a ``Mongo::Database`` | ||
instance and pass the name of the operation to run as a parameter. | ||
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||
The following example calls the ``command`` method to run the ``hello`` command, which | ||
returns information about the server: | ||
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||
.. literalinclude:: /includes/databases-collections/run-command.rb | ||
:language: scala | ||
:dedent: | ||
:start-after: start-hello | ||
:end-before: end-hello | ||
|
||
.. tip:: | ||
|
||
To view a full list of database commands and their corresponding | ||
parameters, see :manual:`Database Commands </reference/command/>` in | ||
the {+mdb-server+} manual. | ||
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Set a Read Preference | ||
---------------------- | ||
|
||
The ``command`` method does not inherit the read preference you might | ||
have set on your ``Database`` instance. By default, ``command`` | ||
uses the ``primary`` read preference. | ||
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You can set a read preference for the command execution by passing a | ||
``ReadPreference`` instance as a parameter to ``command``, as | ||
shown in the following code: | ||
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||
.. literalinclude:: /includes/databases-collections/run-command.rb | ||
:language: scala | ||
:dedent: | ||
:start-after: start-readpref | ||
:end-before: end-readpref | ||
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.. tip:: | ||
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To learn more about read preference options, see :manual:`Read | ||
Preference </core/read-preference/>` in the {+mdb-server+} manual. | ||
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Response | ||
-------- | ||
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The ``command`` method returns a ``Mongo::Operation::Result`` that contains | ||
the response from the database for the given command. | ||
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You can access the fields of the raw command response document by using the following | ||
methods: | ||
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.. list-table:: | ||
:header-rows: 1 | ||
:widths: 30 70 | ||
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* - Method | ||
- Description | ||
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* - ``acknowledged?`` | ||
- Returns ``true`` if the server acknowledged the command, and ``false`` otherwise. | ||
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* - ``inspect`` | ||
- Returns a formatted string representation of the command response. | ||
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* - ``ok?`` | ||
- Returns ``true`` if the command succeeded, and ``false`` otherwise. If the ``ok?`` | ||
method returns ``false``, the driver raises a ``Mongo::Error::OperationFailure`` . | ||
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* - ``cluster_time`` | ||
- Returns the cluster time reported in the server response. Cluster time is a | ||
logical time used for the ordering of operations. This field only | ||
applies to commands run on replica sets or sharded cluster. | ||
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* - ``operation_time`` | ||
- Returns the logical time of the operation execution. | ||
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||
For a full list of methods available on the ``Result`` object, see | ||
the `API documentation <{+api-root+}/Mongo/Operation/Result.html>`__. | ||
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.. tip:: | ||
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To learn more about logical time, see the Wikipedia entry on | ||
the :wikipedia:`logical clock <w/index.php?title=Logical_clock&oldid=1072010149>`. | ||
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Example | ||
~~~~~~~ | ||
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The following example runs the ``dbStats`` command to retrieve | ||
storage statistics for the ``sample_restaurants`` database, then prints the | ||
command results by using the ``inspect`` method: | ||
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.. literalinclude:: /includes/databases-collections/run-command.rb | ||
:language: ruby | ||
:dedent: | ||
:start-after: start-print-command | ||
:end-before: end-print-command | ||
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||
The output of this command includes information about the data stored in | ||
the database, as shown in the following code: | ||
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.. code-block:: none | ||
:copyable: false | ||
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{"db"=>"sample_restaurants", "collections"=>4, "views"=>0, "objects"=>18767, "avgObjSize"=>596.1911866574306, | ||
"dataSize"=>11188720, "storageSize"=>7528448, "totalFreeStorageSize"=>0, "numExtents"=>0, "indexes"=>6, | ||
"indexSize"=>1519616, "indexFreeStorageSize"=>0, "fileSize"=>0, "nsSizeMB"=>0, "ok"=>1} | ||
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Additional Information | ||
---------------------- | ||
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For more information about the concepts in this guide, see the following | ||
documentation in the {+mdb-server+} manual: | ||
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- :manual:`db.runCommand() </reference/method/db.runCommand/>` | ||
- :manual:`Database Commands </reference/command/>` | ||
- :manual:`hello Command </reference/command/hello/>` | ||
- :manual:`dbStats Command </reference/command/dbStats/>` | ||
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API Documentation | ||
~~~~~~~~~~~~~~~~~ | ||
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To learn more about any of the methods or types discussed in this | ||
guide, see the following API documentation: | ||
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||
- `command <{+api-root+}/Mongo/Database.html#command-instance_method>`_ |
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Original file line number | Diff line number | Diff line change |
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require 'bundler/inline' | ||
gemfile do | ||
source 'https://rubygems.org' | ||
gem 'mongo' | ||
end | ||
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uri = "<connection string>" | ||
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Mongo::Client.new(uri) do |client| | ||
# start-db | ||
database = client.use('sample_restaurants') | ||
# end-db | ||
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# start-hello | ||
client.database.command(hello: 1) | ||
# end-hello | ||
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# start-readpref | ||
client.database.command({hello: 1}, read: {mode: :secondary}) | ||
# end-readpref | ||
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# start-print-command | ||
puts client.database.command({dbStats: 1}).first | ||
# end-print-command | ||
end |
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The example given after this paragraph does not use a
ReadPreference
instance, instead passing a hash of read preference options. Maybe the paragraph could be adjusted something like: