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/** @page tut_mongo_sync_cmd_custom Running custom commands
*
* Sometimes it is necessary to run custom commands against a
* database, commands for which the library does not provide a
* convenience wrapper for. In this tutorial, we will explore how to
* run server-side evaluations, using the @a $eval command.
*
* @dontinclude tut_mongo_sync_cmd_custom.c
* @until stdlib.h
*
* @until eval
*
* First, we connect to the database, and create a BSON object that
* will hold our command, one that creates a function server side,
* that takes one argument, and returns the argument plus 4.2. The
* BSON object will also set up the arguments passed to this function,
* which, in our case, will be the number @a 1.
*
* @line conn =
* @until }
*
* @line eval =
* @until bson_finish
*
* Once we have the connection and the query established, it is time
* to send the command:
*
* @line p =
* @until }
*
* We then create a cursor from the returned packet, and iterate over
* it (in case there are multiple documents returned - which will not
* be the case here):
*
* @line cursor =
* @until }
*
* @until gdouble
*
* We want to retrieve each document, and find the @a retval key in
* them, because that's where @a $eval returns the results to us.
*
* @line result =
* @until }
* @until }
*
* At this point, we have successfully extracted the data, so we can
* free up the BSON and cursor objects.
*
* @line bson_cursor_free
* @until bson_free
*
* And finally, print the result:
*
* @until printf
*
* @until }
*
* And that's it! We clean up, disconnect, and that's all there is to
* running custom commands!
*
* @line mongo_sync_cursor_free
* @until }
*/
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