Finding a Document

To query a MongoDB collection with the C driver, use the function mongoc_collection_find(). This returns a cursor to the matching documents. The following examples iterate through the result cursors and print the matches to stdout as JSON strings.

Note that mongoc_collection_find uses a document as a query specifier; for example,

{ "color" : "red" }

will match any document with a field named "color" with value "red". An empty document {} can be used to match all documents.

This first example uses an empty query specifier to find all documents in the database "mydb" and collection "mycoll".

find.c

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

int
main (int   argc,
     char *argv[])
{
  mongoc_client_t *client;
  mongoc_collection_t *collection;
  mongoc_cursor_t *cursor;
  const bson_t *doc;
  bson_t *query;
  char *str;

  mongoc_init ();

  client = mongoc_client_new ("mongodb://localhost:27017/");
  collection = mongoc_client_get_collection (client, "mydb", "mycoll");
  query = bson_new ();
  cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, query, NULL, NULL);

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

  bson_destroy (query);
  mongoc_cursor_destroy (cursor);
  mongoc_collection_destroy (collection);
  mongoc_client_destroy (client);
  mongoc_cleanup ();

  return 0;
}

Compile the code and run it:

$ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

On Windows:

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
C:\> find
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

To look for a specific document, add a specifier to query. This example adds a call to BSON_APPEND_UTF8() to look for all documents matching {"hello" : "world"}.

find-specific.c

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

  int
  main (int   argc,
        char *argv[])
  {
      mongoc_client_t *client;
      mongoc_collection_t *collection;
      mongoc_cursor_t *cursor;
      const bson_t *doc;
      bson_t *query;
      char *str;

      mongoc_init ();

      client = mongoc_client_new ("mongodb://localhost:27017/");
      collection = mongoc_client_get_collection (client, "mydb", "mycoll");
      query = bson_new ();
      BSON_APPEND_UTF8 (query, "hello", "world");

      cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, query, NULL, NULL);

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

      bson_destroy (query);
      mongoc_cursor_destroy (cursor);
      mongoc_collection_destroy (collection);
      mongoc_client_destroy (client);
      mongoc_cleanup ();

      return 0;
  }

$ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }

C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
C:\> find-specific
{ "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }