mongoc_collection_find_with_opts()¶

Synopsis¶

mongoc_cursor_t *
mongoc_collection_find_with_opts (mongoc_collection_t *collection,
                                  const bson_t *filter,
                                  const bson_t *opts,
                                  const mongoc_read_prefs_t *read_prefs)
   BSON_GNUC_WARN_UNUSED_RESULT;

Parameters¶

collection: A mongoc_collection_t.
filter: A bson_t containing the query to execute.
opts: A bson_t query options, including sort order and which fields to return. Can be NULL.
read_prefs: A mongoc_read_prefs_t or NULL.

Description¶

Query on collection, passing arbitrary query options to the server in opts.

To target a specific server, include an integer "serverId" field in opts with an id obtained first by calling mongoc_client_select_server(), then mongoc_server_description_id() on its return value.

Returns¶

A newly allocated mongoc_cursor_t that must be freed with mongoc_cursor_destroy().

Examples¶

Print First Ten Documents in a Collection¶

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

static void
print_ten_documents (mongoc_collection_t *collection)
{
   bson_t *filter;
   bson_t *opts;
   mongoc_cursor_t *cursor;
   bson_error_t error;
   const bson_t *doc;
   char *str;

   /* filter by "foo": 1, order by "bar" descending */
   filter = BCON_NEW ("foo", BCON_INT32 (1));
   opts = BCON_NEW (
      "limit", BCON_INT64 (10), "sort", "{", "bar", BCON_INT32 (-1), "}");

   cursor = mongoc_collection_find_with_opts (collection, filter, opts, NULL);

   while (mongoc_cursor_next (cursor, &doc)) {
      str = bson_as_json (doc, NULL);
      printf ("%s\n", str);
      bson_free (str);
   }

   if (mongoc_cursor_error (cursor, &error)) {
      fprintf (stderr, "An error occurred: %s\n", error.message);
   }

   mongoc_cursor_destroy (cursor);
   bson_destroy (filter);
   bson_destroy (opts);
}

More examples of modifying the query with opts:¶

bson_t *filter;
bson_t *opts;
mongoc_read_prefs_t *read_prefs;

filter = BCON_NEW ("foo", BCON_INT32 (1));

/* Include "field_name_one" and "field_name_two" in "projection", omit
 * others. "_id" must be specifically removed or it is included by default.
 */
opts = BCON_NEW ("projection", "{",
                    "field_name_one", BCON_BOOL (true),
                    "field_name_two", BCON_BOOL (true),
                    "_id", BCON_BOOL (false),
                 "}",
                 "tailable", BCON_BOOL (true),
                 "awaitData", BCON_BOOL (true),
                 "sort", "{", "bar", BCON_INT32 (-1), "}",
                 "collation", "{",
                    "locale", BCON_UTF8("en_US"),
                    "caseFirst", BCON_UTF8 ("lower"),
                 "}");

read_prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);

cursor =
   mongoc_collection_find_with_opts (collection, filter, opts, read_prefs);

The following options are supported.

Option	BSON type	Option	BSON type
`projection`	document	`maxScan`	non-negative int64
`sort`	document	`maxTimeMS`	non-negative int64
`skip`	non-negative int64	`maxAwaitTimeMS`	non-negative int64
`limit`	non-negative int64	`min`	document
`batchSize`	non-negative int64	`noCursorTimeout`	bool
`exhaust`	bool	`oplogReplay`	bool
`hint`	string or document	`returnKey`	bool
`allowPartialResults`	bool	`showRecordId`	bool
`awaitData`	bool	`singleBatch`	bool
`collation`	document	`snapshot`	bool
`comment`	string	`tailable`	bool
`max`	document

All options are documented in the reference page for the "find" command in the MongoDB server manual, except for "maxAwaitTimeMS".

"maxAwaitTimeMS" is the maximum amount of time for the server to wait on new documents to satisfy a query, if "tailable" and "awaitData" are both true. If no new documents are found, the tailable cursor receives an empty batch. The "maxAwaitTimeMS" option is ignored for MongoDB older than 3.4.

For some options like "collation", the driver returns an error if the server version is too old to support the feature. Any fields in opts that are not listed here are passed to the server unmodified.

The "explain" command¶

With MongoDB before 3.2, a query with option $explain: true returns information about the query plan, instead of the query results. Beginning in MongoDB 3.2, there is a separate "explain" command. The driver will not convert "$explain" queries to "explain" commands, you must call the "explain" command explicitly:

/* MongoDB 3.2+, "explain" command syntax */
command = BCON_NEW ("explain", "{",
                    "find", BCON_UTF8 ("collection_name"),
                    "filter", "{", "foo", BCON_INT32 (1), "}",
                    "}");

mongoc_collection_command_simple (collection, command, NULL, &reply, &error);