Provided by: libmongoc-doc_1.21.0-1build1_all bug

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. Not all flag values apply. In particular, setting MONGOC_QUERY_EXHAUST
         results in an error.

       • pipeline: A bson_t, either a BSON array or a BSON document containing an array field named "pipeline".

       • 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: 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: First, construct a mongoc_client_session_t with mongoc_client_start_session. You can begin a
         transaction with mongoc_client_session_start_transaction, optionally  with  a  mongoc_transaction_opt_t
         that  overrides  the options inherited from collection, 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.

       • batchSize:  An  int32  representing  number  of  documents  requested  to  be  returned on each call to
         mongoc_cursor_nextlet: A BSON document consisting of any number of parameter  names,  each  followed  by  definitions  of
         constants in the MQL Aggregate Expression language

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

       This  function  is  considered a retryable read operation unless the pipeline contains a write stage like
       $out or $merge.  Upon a transient error (a network error, errors due to replica set failover,  etc.)  the
       operation  is  safely  retried  once.   If  retryreads  is  false in the URI (see mongoc_uri_t) the retry
       behavior does not apply.

DESCRIPTION

       This function creates a cursor which sends the aggregate command on the underlying  collection  upon  the
       first  call  to  mongoc_cursor_next().  For  more  information on building aggregation pipelines, see the
       MongoDB Manual entry on the aggregate command.

       Read preferences, read and write concern, and  collation  can  be  overridden  by  various  sources.  The
       highest-priority  sources  for  these  options are listed first in the following table. In a transaction,
       read concern and write concern are prohibited in opts and the read preference must be  primary  or  NULL.
       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.

                             ┌─────────────────┬──────────────┬───────────────┬───────────┐
                             │Read Preferences │ Read Concern │ Write Concern │ Collation │
                             ├─────────────────┼──────────────┼───────────────┼───────────┤
                             │read_prefsoptsoptsopts      │
                             ├─────────────────┼──────────────┼───────────────┼───────────┤
                             │Transaction      │ Transaction  │ Transaction   │           │
                             ├─────────────────┼──────────────┼───────────────┼───────────┤
                             │collectioncollectioncollection    │           │
                             └─────────────────┴──────────────┴───────────────┴───────────┘

       See the example for transactions and for the "distinct" command with opts.

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, even on  error.  The  user  must  call
       mongoc_cursor_next() on the returned mongoc_cursor_t to execute the initial command.

       Cursor  errors  can be checked with mongoc_cursor_error_document. It always fills out the bson_error_t if
       an error occurred, and optionally includes a server reply document if the error occurred server-side.

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

EXAMPLE

          #include <bson/bson.h>
          #include <mongoc/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

       2017-present, MongoDB, Inc