mongoc_collection_count_documents()

Synopsis

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

Parameters

• collection: A mongoc_collection_t.
• filter: A bson_t containing the filter.
• opts: A bson_t, NULL to ignore.
• read_prefs: A mongoc_read_prefs_t or NULL.
• reply: A location for an uninitialized bson_t to store the command reply, NULL to ignore. If not NULL, reply will be initialized.
• 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. Only string values are supported prior to MongoDB 4.4.
• hint: A document or string that specifies the index to use to support the query predicate.

Other options are included in the sent aggregate command. For a list of all options, see the MongoDB Manual entry on the aggregate command.

Description

This functions executes a count query on collection. In contrast with mongoc_collection_estimated_document_count(), the count returned is 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.

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 *filter)
{
   bson_error_t error;
   int64_t count;
   bson_t* opts = BCON_NEW ("skip", BCON_INT64(5));

   count = mongoc_collection_count_documents (
      collection, filter, 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);
   }
}

Migrating from deprecated count functions

When migrating to mongoc_collection_count_documents() from the deprecated mongoc_collection_count() or mongoc_collection_count_with_opts(), the following query operators in the filter must be replaced:

Operator	Replacement
$where	$expr
$near	$geoWithin with $center
$nearSphere	$geoWithin with $centerSphere

$expr requires MongoDB 3.6+

See also

mongoc_collection_estimated_document_count()