noble (3) mongoc_collection_estimated_document_count.3.gz

SYNOPSIS

          int64_t
          mongoc_collection_estimated_document_count (mongoc_collection_t *collection,
                                                      const bson_t *opts,
                                                      const mongoc_read_prefs_t *read_prefs,
                                                      bson_t *reply,
                                                      bson_error_t *error);

PARAMETERS

       • collection: A mongoc_collection_t.

       • opts: A bson_t, NULL to ignore.

       • read_prefs: A mongoc_read_prefs_t or NULL.

       • reply: A maybe-NULL pointer to overwritable storage for a bson_t to contain the results.

       • error: An optional location for a bson_error_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.

       • 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.

       • 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.

       • skip: An int specifying how many documents matching the query should be skipped before counting.

       • limit: An int specifying the maximum number of documents to count.

       • comment:  A  bson_value_t  specifying the comment to attach to this command. The comment will appear in
         log messages, profiler output, and currentOp output. Requires MongoDB 4.4 or later.

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

DESCRIPTION

       This    functions    executes    a    count     query     on     collection.     In     contrast     with
       mongoc_collection_count_documents(), the count returned is not guaranteed to be accurate.

       This  function is considered a retryable read operation.  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.

   Behavior
       This  method  is  implemented  using  the  count  command. Due to an oversight in versions 5.0.0-5.0.8 of
       MongoDB, the count command was not included in version "1" of the Stable  API.  Applications  using  this
       method  with  the  Stable API are recommended to upgrade their server version to 5.0.9+ or disable strict
       mode (via :symbol:`mongoc_server_api_strict()) to avoid encountering errors.

ERRORS

       Errors are propagated via the error parameter.

RETURNS

       -1 on failure, otherwise the number of documents counted.

EXAMPLE

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

          static void
          print_count (mongoc_collection_t *collection, bson_t *query)
          {
             bson_error_t error;
             int64_t count;
             bson_t* opts = BCON_NEW ("skip", BCON_INT64(5));

             count = mongoc_collection_estimated_document_count (
                collection, opts, NULL, NULL, &error);
             bson_destroy (opts);

             if (count < 0) {
                fprintf (stderr, "Count failed: %s\n", error.message);
             } else {
                printf ("%" PRId64 " documents counted.\n", count);
             }
          }

       SEE ALSO:
          mongoc_collection_count_documents()
          Count: Behavior in the MongoDB Manual

AUTHOR

       MongoDB, Inc

COPYRIGHT

       2017-present, MongoDB, Inc