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.\" 
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.\" under the terms of the GNU Free Documentation License, Version 1.3
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.TH "MONGOC_COLLECTION_AGGREGATE" "3" "2016\(hy10\(hy12" "MongoDB C Driver"
.SH NAME
mongoc_collection_aggregate() \- This function shall execute an aggregation query on the underlying 'collection'. The bson 'pipeline' is not validated, simply passed along as appropriate to the server.  As such, compatibility and errors should be validated in the appropriate server documentation.
.SH "SYNOPSIS"

.nf
.nf
mongoc_cursor_t *
mongoc_collection_aggregate (mongoc_collection_t       *collection,
                             mongoc_query_flags_t       flags,
                             const bson_t              *pipeline,
                             const bson_t              *options,
                             const mongoc_read_prefs_t *read_prefs)
   BSON_GNUC_WARN_UNUSED_RESULT;
.fi
.fi

.SH "PARAMETERS"

.TP
.B
collection
A
.B mongoc_collection_t
.
.LP
.TP
.B
flags
A
.B mongoc_query_flags_t
.
.LP
.TP
.B
pipeline
A
.B bson_t
containing the pipeline array.
.LP
.TP
.B
options
A
.B bson_t
containing options for the pipeline, or
.B NULL
.
.LP
.TP
.B
read_prefs
A
.B mongoc_read_prefs_t
or
.B NULL
.
.LP

.SH "DESCRIPTION"

This function shall execute an aggregation query on the underlying 'collection'. The bson 'pipeline' is not validated, simply passed along as appropriate to the server. As such, compatibility and errors should be validated in the appropriate server documentation.

In the case of older server versions, < v2.5, the returned cursor is a synthetic iterator over the result set. This provides a limitation insofar as returned documents can be no larger than 16MB. When connecting to newer servers this limitation doesn't exist. The specific test is for wire_version > 0.

For more information on building MongoDB pipelines, see
.B MongoDB Aggregation Command
on the MongoDB website.

.B NOTE
.RS
The
.B pipeline
parameter should contain a field named
.B pipeline
containing a BSON array of pipeline stages.
.RE

.B NOTE
.RS
The
.B mongoc_read_concern_t
specified on the
.B mongoc_collection_t
will be used, if any.
.RE

.SH "RETURNS"

This function returns a newly allocated
.B mongoc_cursor_t
that should be freed with
.B mongoc_cursor_destroy(3)
when no longer in use.
.B NULL
may be returned if parameters are invalid.

.B NOTE
.RS
Failure to handle the result of this function is a programming error.
.RE

.SH "EXAMPLE"

.nf
#include <bcon.h>
#include <mongoc.h>

static mongoc_cursor_t *
pipeline_query (mongoc_collection_t *collection)
{
   mongoc_cursor_t *cursor;
   bson_t *pipeline;

   pipeline = BCON_NEW ("pipeline", "[",
                           "{", "$match", "{", "foo", BCON_UTF8 ("A"), "}", "}",
                           "{", "$match", "{", "bar", BCON_BOOL (false), "}", "}",
                        "]");

   cursor = mongoc_collection_aggregate (collection,
                                         MONGOC_QUERY_NONE,
                                         pipeline,
                                         NULL,
                                         NULL);

   bson_destroy (pipeline);

   return cursor;
}
.fi

.SH "OTHER PARAMETERS"

Pass any parameters to the
.B aggregate
command, besides
.B pipeline
, as fields in
.B options
:

.nf
pipeline = BCON_NEW ("pipeline", "[",
                        "{", "$out", BCON_UTF8 ("collection2"), "}",
                     "]");

options = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
cursor = mongoc_collection_aggregate (collection1,
                                      MONGOC_QUERY_NONE,
                                      pipeline,
                                      options,
                                      NULL);
.fi


.B
.SH COLOPHON
This page is part of MongoDB C Driver.
Please report any bugs at https://jira.mongodb.org/browse/CDRIVER.