NAME

       mongoc_collection_aggregate - mongoc_collection_aggregate()

SYNOPSIS

          mongoc_cursor_t *
          mongoc_collection_aggregate (mongoc_collection_t *collection,
                                       mongoc_query_flags_t flags,
                                       const bson_t *pipeline,
                                       const bson_t *opts,
                                       const mongoc_read_prefs_t *read_prefs)
             BSON_GNUC_WARN_UNUSED_RESULT;

PARAMETERS

       • collection: A mongoc_collection_t.

       • flags: A mongoc_query_flags_t.

       • pipeline: A bson_t containing the pipeline array.

       • opts: A bson_t containing options for the command, or NULL.

       • read_prefs: A mongoc_read_prefs_t or NULL.

       opts may be NULL or a BSON document with additional command options:

       • readConcern:  Construct  a  mongoc_read_concern_t  and  use  mongoc_read_concern_append to add the read
         concern to opts. See the example code for mongoc_client_read_command_with_opts. Read  concern  requires
         MongoDB 3.2 or later, otherwise an error is returned.

       • writeConcern:  For aggregations that include "$out", you can construct a mongoc_write_concern_t and use
         mongoc_write_concern_append  to  add  the  write  concern  to  opts.   See   the   example   code   for
         mongoc_client_write_command_with_opts.

       • sessionId:    Construct    a   mongoc_client_session_t   with   mongoc_client_start_session   and   use
         mongoc_client_session_append   to   add   the   session   to   opts.   See   the   example   code   for
         mongoc_client_session_t.

       • bypassDocumentValidation:  Set  to  true  to  skip  server-side  schema validation of the provided BSON
         documents.

       • collation: Configure textual comparisons. See Setting Collation Order, and the MongoDB Manual entry  on
         Collation. Collation requires MongoDB 3.2 or later, otherwise an error is returned.

       • serverId:  To  target  a  specific  server, include an int32 "serverId" field. Obtain the id by calling
         mongoc_client_select_server, then mongoc_server_description_id on its return value.

       For a list of all options, see the MongoDB Manual entry on the aggregate command.

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.

       For more information on building MongoDB pipelines,  see  the  MongoDB  Manual  entry  on  the  aggregate
       command.

       NOTE:
          The  pipeline  parameter  should  contain  a  field named pipeline containing a BSON array of pipeline
          stages.

       Read concern is applied from opts or else from collection. Collation is applied from  opts  (see  example
       for  the  "distinct"  command  with  opts).  Read  preferences  are  applied from read_prefs or else from
       collection. Write concern is applied from opts, or if opts has  no  write  concern  and  the  aggregation
       pipeline  includes "$out", the write concern is applied from collection. The write concern is omitted for
       MongoDB before 3.4.

RETURNS

       This function returns a newly allocated mongoc_cursor_t that should be freed with mongoc_cursor_destroy()
       when  no  longer  in  use. The returned mongoc_cursor_t is never NULL; if the parameters are invalid, the
       bson_error_t in the mongoc_cursor_t is filled out, and the mongoc_cursor_t is returned before the  server
       is selected.

       WARNING:
          Failure to handle the result of this function is a programming error.

EXAMPLE

          #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;
          }

OTHER PARAMETERS

       When  using  $out, the pipeline stage that writes, the write_concern field of the mongoc_cursor_t will be
       set to the mongoc_write_concern_t parameter, if it is valid,  and  applied  to  the  write  command  when
       mongoc_cursor_next()  is called. Pass any other parameters to the aggregate command, besides pipeline, as
       fields in opts:

          mongoc_write_concern_t *write_concern = mongoc_write_concern_new ();
          mongoc_write_concern_set_w (write_concern, 3);

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

          opts = BCON_NEW ("bypassDocumentValidation", BCON_BOOL (true));
          mongoc_write_concern_append (write_concern, opts);

          cursor = mongoc_collection_aggregate (
             collection1, MONGOC_QUERY_NONE, pipeline, opts, NULL);

AUTHOR

       MongoDB, Inc

COPYRIGHT

       2018, MongoDB, Inc