1MONGOC_TUTORIAL(3) libmongoc MONGOC_TUTORIAL(3)
2
6 mongoc_tutorial - Tutorial
7 This guide offers a brief introduction to the MongoDB C Driver.
9 For more information on the C API, please refer to the api.
11 Contents
13 · Tutorial
14 · Installing
16 · Starting MongoDB
18 · Include and link libmongoc in your C program
20 · Use libmongoc in a Microsoft Visual Studio Project
22 · Making a Connection
24 · Creating BSON Documents
26 · Basic CRUD Operations
28 · Executing Commands
30 · Threading
32 · Next Steps
34
36 For detailed instructions on installing the MongoDB C Driver on a par‐
37 ticular platform, please see the installation guide.
38
40 To run the examples in this tutorial, MongoDB must be installed and
41 running on localhost on the default port, 27017. To check if it is up
42 and running, connect to it with the MongoDB shell.
43 $ mongo --host localhost --port 27017
45 MongoDB shell version: 3.0.6
46 connecting to: localhost:27017/test
47 >
48
50 Include mongoc.h
51 All libmongoc's functions and types are available in one header file.
52 Simply include mongoc/mongoc.h:
53 #include <mongoc/mongoc.h>
55 CMake
57 The libmongoc installation includes a CMake config-file package, so you
58 can use CMake's find_package command to import libmongoc's CMake target
59 and link to libmongoc (as a shared library):
60 CMakeLists.txt
62 # Specify the minimum version you require.
64 find_package (mongoc-1.0 1.7 REQUIRED)
65 # The "hello_mongoc.c" sample program is shared among four tests.
67 add_executable (hello_mongoc ../../hello_mongoc.c)
68 target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_shared)
69 You can also use libmongoc as a static library instead: Use the
72 mongo::mongoc_static CMake target:
73 # Specify the minimum version you require.
75 find_package (mongoc-1.0 1.7 REQUIRED)
76 # The "hello_mongoc.c" sample program is shared among four tests.
78 add_executable (hello_mongoc ../../hello_mongoc.c)
79 target_link_libraries (hello_mongoc PRIVATE mongo::mongoc_static)
80 pkg-config
83 If you're not using CMake, use pkg-config on the command line to set
84 header and library paths:
85 gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-1.0)
87 Or to statically link to libmongoc:
90 gcc -o hello_mongoc hello_mongoc.c $(pkg-config --libs --cflags libmongoc-static-1.0)
92 Specifying header and include paths manually
95 If you aren't using CMake or pkg-config, paths and libraries can be
96 managed manually.
97 $ gcc -o hello_mongoc hello_mongoc.c \
99 -I/usr/local/include/libbson-1.0 -I/usr/local/include/libmongoc-1.0 \
100 -lmongoc-1.0 -lbson-1.0
101 $ ./hello_mongoc
102 { "ok" : 1.000000 }
103 For Windows users, the code can be compiled and run with the following
105 commands. (This assumes that the MongoDB C Driver has been installed to
106 C:\mongo-c-driver; change the include directory as needed.)
107 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 hello_mongoc.c
109 C:\> hello_mongoc
110 { "ok" : 1.000000 }
111
113 See the libmongoc and Visual Studio guide.
114
116 Access MongoDB with a mongoc_client_t. It transparently connects to
117 standalone servers, replica sets and sharded clusters on demand. To
118 perform operations on a database or collection, create a mongoc_data‐
119 base_t or mongoc_collection_t struct from the mongoc_client_t.
120 At the start of an application, call mongoc_init before any other lib‐
122 mongoc functions. At the end, call the appropriate destroy function for
123 each collection, database, or client handle, in reverse order from how
124 they were constructed. Call mongoc_cleanup before exiting.
125 The example below establishes a connection to a standalone server on
127 localhost, registers the client application as "connect-example," and
128 performs a simple command.
129 More information about database operations can be found in the CRUD
131 Operations and Executing Commands sections. Examples of connecting to
132 replica sets and sharded clusters can be found on the Advanced Connec‐
133 tions page.
134 hello_mongoc.c
136 #include <mongoc/mongoc.h>
138 int
140 main (int argc, char *argv[])
141 {
142 const char *uri_string = "mongodb://localhost:27017";
143 mongoc_uri_t *uri;
144 mongoc_client_t *client;
145 mongoc_database_t *database;
146 mongoc_collection_t *collection;
147 bson_t *command, reply, *insert;
148 bson_error_t error;
149 char *str;
150 bool retval;
151 /*
153 * Required to initialize libmongoc's internals
154 */
155 mongoc_init ();
156 /*
158 * Optionally get MongoDB URI from command line
159 */
160 if (argc > 1) {
161 uri_string = argv[1];
162 }
163 /*
165 * Safely create a MongoDB URI object from the given string
166 */
167 uri = mongoc_uri_new_with_error (uri_string, &error);
168 if (!uri) {
169 fprintf (stderr,
170 "failed to parse URI: %s\n"
171 "error message: %s\n",
172 uri_string,
173 error.message);
174 return EXIT_FAILURE;
175 }
176 /*
178 * Create a new client instance
179 */
180 client = mongoc_client_new_from_uri (uri);
181 if (!client) {
182 return EXIT_FAILURE;
183 }
184 /*
186 * Register the application name so we can track it in the profile logs
187 * on the server. This can also be done from the URI (see other examples).
188 */
189 mongoc_client_set_appname (client, "connect-example");
190 /*
192 * Get a handle on the database "db_name" and collection "coll_name"
193 */
194 database = mongoc_client_get_database (client, "db_name");
195 collection = mongoc_client_get_collection (client, "db_name", "coll_name");
196 /*
198 * Do work. This example pings the database, prints the result as JSON and
199 * performs an insert
200 */
201 command = BCON_NEW ("ping", BCON_INT32 (1));
202 retval = mongoc_client_command_simple (
204 client, "admin", command, NULL, &reply, &error);
205 if (!retval) {
207 fprintf (stderr, "%s\n", error.message);
208 return EXIT_FAILURE;
209 }
210 str = bson_as_json (&reply, NULL);
212 printf ("%s\n", str);
213 insert = BCON_NEW ("hello", BCON_UTF8 ("world"));
215 if (!mongoc_collection_insert_one (collection, insert, NULL, NULL, &error)) {
217 fprintf (stderr, "%s\n", error.message);
218 }
219 bson_destroy (insert);
221 bson_destroy (&reply);
222 bson_destroy (command);
223 bson_free (str);
224 /*
226 * Release our handles and clean up libmongoc
227 */
228 mongoc_collection_destroy (collection);
229 mongoc_database_destroy (database);
230 mongoc_uri_destroy (uri);
231 mongoc_client_destroy (client);
232 mongoc_cleanup ();
233 return EXIT_SUCCESS;
235 }
236
239 Documents are stored in MongoDB's data format, BSON. The C driver uses
240 libbson to create BSON documents. There are several ways to construct
241 them: appending key-value pairs, using BCON, or parsing JSON.
242 Appending BSON
244 A BSON document, represented as a bson_t in code, can be constructed
245 one field at a time using libbson's append functions.
246 For example, to create a document like this:
248 {
250 born : ISODate("1906-12-09"),
251 died : ISODate("1992-01-01"),
252 name : {
253 first : "Grace",
254 last : "Hopper"
255 },
256 languages : [ "MATH-MATIC", "FLOW-MATIC", "COBOL" ],
257 degrees: [ { degree: "BA", school: "Vassar" }, { degree: "PhD", school: "Yale" } ]
258 }
259 Use the following code:
261 #include <bson/bson.h>
263 int
265 main (int argc,
266 char *argv[])
267 {
268 struct tm born = { 0 };
269 struct tm died = { 0 };
270 const char *lang_names[] = {"MATH-MATIC", "FLOW-MATIC", "COBOL"};
271 const char *schools[] = {"Vassar", "Yale"};
272 const char *degrees[] = {"BA", "PhD"};
273 uint32_t i;
274 char buf[16];
275 const char *key;
276 size_t keylen;
277 bson_t *document;
278 bson_t child;
279 bson_t child2;
280 char *str;
281 document = bson_new ();
283 /*
285 * Append { "born" : ISODate("1906-12-09") } to the document.
286 * Passing -1 for the length argument tells libbson to calculate the string length.
287 */
288 born.tm_year = 6; /* years are 1900-based */
289 born.tm_mon = 11; /* months are 0-based */
290 born.tm_mday = 9;
291 bson_append_date_time (document, "born", -1, mktime (&born) * 1000);
292 /*
294 * Append { "died" : ISODate("1992-01-01") } to the document.
295 */
296 died.tm_year = 92;
297 died.tm_mon = 0;
298 died.tm_mday = 1;
299 /*
301 * For convenience, this macro passes length -1 by default.
302 */
303 BSON_APPEND_DATE_TIME (document, "died", mktime (&died) * 1000);
304 /*
306 * Append a subdocument.
307 */
308 BSON_APPEND_DOCUMENT_BEGIN (document, "name", &child);
309 BSON_APPEND_UTF8 (&child, "first", "Grace");
310 BSON_APPEND_UTF8 (&child, "last", "Hopper");
311 bson_append_document_end (document, &child);
312 /*
314 * Append array of strings. Generate keys "0", "1", "2".
315 */
316 BSON_APPEND_ARRAY_BEGIN (document, "languages", &child);
317 for (i = 0; i < sizeof lang_names / sizeof (char *); ++i) {
318 keylen = bson_uint32_to_string (i, &key, buf, sizeof buf);
319 bson_append_utf8 (&child, key, (int) keylen, lang_names[i], -1);
320 }
321 bson_append_array_end (document, &child);
322 /*
324 * Array of subdocuments:
325 * degrees: [ { degree: "BA", school: "Vassar" }, ... ]
326 */
327 BSON_APPEND_ARRAY_BEGIN (document, "degrees", &child);
328 for (i = 0; i < sizeof degrees / sizeof (char *); ++i) {
329 keylen = bson_uint32_to_string (i, &key, buf, sizeof buf);
330 bson_append_document_begin (&child, key, (int) keylen, &child2);
331 BSON_APPEND_UTF8 (&child2, "degree", degrees[i]);
332 BSON_APPEND_UTF8 (&child2, "school", schools[i]);
333 bson_append_document_end (&child, &child2);
334 }
335 bson_append_array_end (document, &child);
336 /*
338 * Print the document as a JSON string.
339 */
340 str = bson_as_canonical_extended_json (document, NULL);
341 printf ("%s\n", str);
342 bson_free (str);
343 /*
345 * Clean up allocated bson documents.
346 */
347 bson_destroy (document);
348 return 0;
349 }
350 See the libbson documentation for all of the types that can be appended
352 to a bson_t.
353 Using BCON
355 BSON C Object Notation, BCON for short, is an alternative way of con‐
356 structing BSON documents in a manner closer to the intended format. It
357 has less type-safety than BSON's append functions but results in less
358 code.
359 #include <bson/bson.h>
361 int
363 main (int argc,
364 char *argv[])
365 {
366 struct tm born = { 0 };
367 struct tm died = { 0 };
368 bson_t *document;
369 char *str;
370 born.tm_year = 6;
372 born.tm_mon = 11;
373 born.tm_mday = 9;
374 died.tm_year = 92;
376 died.tm_mon = 0;
377 died.tm_mday = 1;
378 document = BCON_NEW (
380 "born", BCON_DATE_TIME (mktime (&born) * 1000),
381 "died", BCON_DATE_TIME (mktime (&died) * 1000),
382 "name", "{",
383 "first", BCON_UTF8 ("Grace"),
384 "last", BCON_UTF8 ("Hopper"),
385 "}",
386 "languages", "[",
387 BCON_UTF8 ("MATH-MATIC"),
388 BCON_UTF8 ("FLOW-MATIC"),
389 BCON_UTF8 ("COBOL"),
390 "]",
391 "degrees", "[",
392 "{", "degree", BCON_UTF8 ("BA"), "school", BCON_UTF8 ("Vassar"), "}",
393 "{", "degree", BCON_UTF8 ("PhD"), "school", BCON_UTF8 ("Yale"), "}",
394 "]");
395 /*
397 * Print the document as a JSON string.
398 */
399 str = bson_as_canonical_extended_json (document, NULL);
400 printf ("%s\n", str);
401 bson_free (str);
402 /*
404 * Clean up allocated bson documents.
405 */
406 bson_destroy (document);
407 return 0;
408 }
409 Notice that BCON can create arrays, subdocuments and arbitrary fields.
411 Creating BSON from JSON
413 For single documents, BSON can be created from JSON strings via
414 bson_new_from_json.
415 #include <bson/bson.h>
417 int
419 main (int argc,
420 char *argv[])
421 {
422 bson_error_t error;
423 bson_t *bson;
424 char *string;
425 const char *json = "{\"name\": {\"first\":\"Grace\", \"last\":\"Hopper\"}}";
427 bson = bson_new_from_json ((const uint8_t *)json, -1, &error);
428 if (!bson) {
430 fprintf (stderr, "%s\n", error.message);
431 return EXIT_FAILURE;
432 }
433 string = bson_as_canonical_extended_json (bson, NULL);
435 printf ("%s\n", string);
436 bson_free (string);
437 return 0;
439 }
440 To initialize BSON from a sequence of JSON documents, use
442 bson_json_reader_t.
443
445 This section demonstrates the basics of using the C Driver to interact
446 with MongoDB.
447 Inserting a Document
449 To insert documents into a collection, first obtain a handle to a mon‐
450 goc_collection_t via a mongoc_client_t. Then, use mongoc_collec‐
451 tion_insert_one to add BSON documents to the collection. This example
452 inserts into the database "mydb" and collection "mycoll".
453 When finished, ensure that allocated structures are freed by using
455 their respective destroy functions.
456 #include <bson/bson.h>
458 #include <mongoc/mongoc.h>
459 #include <stdio.h>
460 int
462 main (int argc,
463 char *argv[])
464 {
465 mongoc_client_t *client;
466 mongoc_collection_t *collection;
467 bson_error_t error;
468 bson_oid_t oid;
469 bson_t *doc;
470 mongoc_init ();
472 client = mongoc_client_new ("mongodb://localhost:27017/?appname=insert-example");
474 collection = mongoc_client_get_collection (client, "mydb", "mycoll");
475 doc = bson_new ();
477 bson_oid_init (&oid, NULL);
478 BSON_APPEND_OID (doc, "_id", &oid);
479 BSON_APPEND_UTF8 (doc, "hello", "world");
480 if (!mongoc_collection_insert_one (
482 collection, doc, NULL, NULL, &error)) {
483 fprintf (stderr, "%s\n", error.message);
484 }
485 bson_destroy (doc);
487 mongoc_collection_destroy (collection);
488 mongoc_client_destroy (client);
489 mongoc_cleanup ();
490 return 0;
492 }
493 Compile the code and run it:
495 $ gcc -o insert insert.c $(pkg-config --cflags --libs libmongoc-1.0)
497 $ ./insert
498 On Windows:
500 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 insert.c
502 C:\> insert
503 To verify that the insert succeeded, connect with the MongoDB shell.
505 $ mongo
507 MongoDB shell version: 3.0.6
508 connecting to: test
509 > use mydb
510 switched to db mydb
511 > db.mycoll.find()
512 { "_id" : ObjectId("55ef43766cb5f36a3bae6ee4"), "hello" : "world" }
513 >
514 Finding a Document
516 To query a MongoDB collection with the C driver, use the function mon‐
517 goc_collection_find_with_opts(). This returns a cursor to the matching
518 documents. The following examples iterate through the result cursors
519 and print the matches to stdout as JSON strings.
520 Use a document as a query specifier; for example,
522 { "color" : "red" }
524 will match any document with a field named "color" with value "red". An
526 empty document {} can be used to match all documents.
527 This first example uses an empty query specifier to find all documents
529 in the database "mydb" and collection "mycoll".
530 #include <bson/bson.h>
532 #include <mongoc/mongoc.h>
533 #include <stdio.h>
534 int
536 main (int argc, char *argv[])
537 {
538 mongoc_client_t *client;
539 mongoc_collection_t *collection;
540 mongoc_cursor_t *cursor;
541 const bson_t *doc;
542 bson_t *query;
543 char *str;
544 mongoc_init ();
546 client =
548 mongoc_client_new ("mongodb://localhost:27017/?appname=find-example");
549 collection = mongoc_client_get_collection (client, "mydb", "mycoll");
550 query = bson_new ();
551 cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
552 while (mongoc_cursor_next (cursor, &doc)) {
554 str = bson_as_canonical_extended_json (doc, NULL);
555 printf ("%s\n", str);
556 bson_free (str);
557 }
558 bson_destroy (query);
560 mongoc_cursor_destroy (cursor);
561 mongoc_collection_destroy (collection);
562 mongoc_client_destroy (client);
563 mongoc_cleanup ();
564 return 0;
566 }
567 Compile the code and run it:
569 $ gcc -o find find.c $(pkg-config --cflags --libs libmongoc-1.0)
571 $ ./find
572 { "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
573 On Windows:
575 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find.c
577 C:\> find
578 { "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
579 To look for a specific document, add a specifier to query. This example
581 adds a call to BSON_APPEND_UTF8() to look for all documents matching
582 {"hello" : "world"}.
583 #include <bson/bson.h>
585 #include <mongoc/mongoc.h>
586 #include <stdio.h>
587 int
589 main (int argc, char *argv[])
590 {
591 mongoc_client_t *client;
592 mongoc_collection_t *collection;
593 mongoc_cursor_t *cursor;
594 const bson_t *doc;
595 bson_t *query;
596 char *str;
597 mongoc_init ();
599 client = mongoc_client_new (
601 "mongodb://localhost:27017/?appname=find-specific-example");
602 collection = mongoc_client_get_collection (client, "mydb", "mycoll");
603 query = bson_new ();
604 BSON_APPEND_UTF8 (query, "hello", "world");
605 cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
607 while (mongoc_cursor_next (cursor, &doc)) {
609 str = bson_as_canonical_extended_json (doc, NULL);
610 printf ("%s\n", str);
611 bson_free (str);
612 }
613 bson_destroy (query);
615 mongoc_cursor_destroy (cursor);
616 mongoc_collection_destroy (collection);
617 mongoc_client_destroy (client);
618 mongoc_cleanup ();
619 return 0;
621 }
622 $ gcc -o find-specific find-specific.c $(pkg-config --cflags --libs libmongoc-1.0)
624 $ ./find-specific
625 { "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
626 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 find-specific.c
628 C:\> find-specific
629 { "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
630 Updating a Document
632 This code snippet gives an example of using mongoc_collec‐
633 tion_update_one() to update the fields of a document.
634 Using the "mydb" database, the following example inserts an example
636 document into the "mycoll" collection. Then, using its _id field, the
637 document is updated with different values and a new field.
638 #include <bson/bson.h>
640 #include <mongoc/mongoc.h>
641 #include <stdio.h>
642 int
644 main (int argc, char *argv[])
645 {
646 mongoc_collection_t *collection;
647 mongoc_client_t *client;
648 bson_error_t error;
649 bson_oid_t oid;
650 bson_t *doc = NULL;
651 bson_t *update = NULL;
652 bson_t *query = NULL;
653 mongoc_init ();
655 client =
657 mongoc_client_new ("mongodb://localhost:27017/?appname=update-example");
658 collection = mongoc_client_get_collection (client, "mydb", "mycoll");
659 bson_oid_init (&oid, NULL);
661 doc = BCON_NEW ("_id", BCON_OID (&oid), "key", BCON_UTF8 ("old_value"));
662 if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
664 fprintf (stderr, "%s\n", error.message);
665 goto fail;
666 }
667 query = BCON_NEW ("_id", BCON_OID (&oid));
669 update = BCON_NEW ("$set",
670 "{",
671 "key",
672 BCON_UTF8 ("new_value"),
673 "updated",
674 BCON_BOOL (true),
675 "}");
676 if (!mongoc_collection_update_one (
678 collection, query, update, NULL, NULL, &error)) {
679 fprintf (stderr, "%s\n", error.message);
680 goto fail;
681 }
682 fail:
684 if (doc)
685 bson_destroy (doc);
686 if (query)
687 bson_destroy (query);
688 if (update)
689 bson_destroy (update);
690 mongoc_collection_destroy (collection);
692 mongoc_client_destroy (client);
693 mongoc_cleanup ();
694 return 0;
696 }
697 Compile the code and run it:
699 $ gcc -o update update.c $(pkg-config --cflags --libs libmongoc-1.0)
701 $ ./update
702 On Windows:
704 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 update.c
706 C:\> update
707 { "_id" : { "$oid" : "55ef43766cb5f36a3bae6ee4" }, "hello" : "world" }
708 To verify that the update succeeded, connect with the MongoDB shell.
710 $ mongo
712 MongoDB shell version: 3.0.6
713 connecting to: test
714 > use mydb
715 switched to db mydb
716 > db.mycoll.find({"updated" : true})
717 { "_id" : ObjectId("55ef549236fe322f9490e17b"), "updated" : true, "key" : "new_value" }
718 >
719 Deleting a Document
721 This example illustrates the use of mongoc_collection_delete_one() to
722 delete a document.
723 The following code inserts a sample document into the database "mydb"
725 and collection "mycoll". Then, it deletes all documents matching
726 {"hello" : "world"}.
727 #include <bson/bson.h>
729 #include <mongoc/mongoc.h>
730 #include <stdio.h>
731 int
733 main (int argc, char *argv[])
734 {
735 mongoc_client_t *client;
736 mongoc_collection_t *collection;
737 bson_error_t error;
738 bson_oid_t oid;
739 bson_t *doc;
740 mongoc_init ();
742 client =
744 mongoc_client_new ("mongodb://localhost:27017/?appname=delete-example");
745 collection = mongoc_client_get_collection (client, "test", "test");
746 doc = bson_new ();
748 bson_oid_init (&oid, NULL);
749 BSON_APPEND_OID (doc, "_id", &oid);
750 BSON_APPEND_UTF8 (doc, "hello", "world");
751 if (!mongoc_collection_insert_one (collection, doc, NULL, &error)) {
753 fprintf (stderr, "Insert failed: %s\n", error.message);
754 }
755 bson_destroy (doc);
757 doc = bson_new ();
759 BSON_APPEND_OID (doc, "_id", &oid);
760 if (!mongoc_collection_delete_one (
762 collection, doc, NULL, NULL, &error)) {
763 fprintf (stderr, "Delete failed: %s\n", error.message);
764 }
765 bson_destroy (doc);
767 mongoc_collection_destroy (collection);
768 mongoc_client_destroy (client);
769 mongoc_cleanup ();
770 return 0;
772 }
773 Compile the code and run it:
775 $ gcc -o delete delete.c $(pkg-config --cflags --libs libmongoc-1.0)
777 $ ./delete
778 On Windows:
780 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 delete.c
782 C:\> delete
783 Use the MongoDB shell to prove that the documents have been removed
785 successfully.
786 $ mongo
788 MongoDB shell version: 3.0.6
789 connecting to: test
790 > use mydb
791 switched to db mydb
792 > db.mycoll.count({"hello" : "world"})
793 0
794 >
795 Counting Documents
797 Counting the number of documents in a MongoDB collection is similar to
798 performing a find operation. This example counts the number of docu‐
799 ments matching {"hello" : "world"} in the database "mydb" and collec‐
800 tion "mycoll".
801 #include <bson/bson.h>
803 #include <mongoc/mongoc.h>
804 #include <stdio.h>
805 int
807 main (int argc, char *argv[])
808 {
809 mongoc_client_t *client;
810 mongoc_collection_t *collection;
811 bson_error_t error;
812 bson_t *doc;
813 int64_t count;
814 mongoc_init ();
816 client =
818 mongoc_client_new ("mongodb://localhost:27017/?appname=count-example");
819 collection = mongoc_client_get_collection (client, "mydb", "mycoll");
820 doc = bson_new_from_json (
821 (const uint8_t *) "{\"hello\" : \"world\"}", -1, &error);
822 count = mongoc_collection_count (
824 collection, MONGOC_QUERY_NONE, doc, 0, 0, NULL, &error);
825 if (count < 0) {
827 fprintf (stderr, "%s\n", error.message);
828 } else {
829 printf ("%" PRId64 "\n", count);
830 }
831 bson_destroy (doc);
833 mongoc_collection_destroy (collection);
834 mongoc_client_destroy (client);
835 mongoc_cleanup ();
836 return 0;
838 }
839 Compile the code and run it:
841 $ gcc -o count count.c $(pkg-config --cflags --libs libmongoc-1.0)
843 $ ./count
844 1
845 On Windows:
847 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 count.c
849 C:\> count
850 1
851
853 The driver provides helper functions for executing MongoDB commands on
854 client, database and collection structures. These functions return cur‐
855 sors; the _simple variants return booleans indicating success or fail‐
856 ure.
857 This example executes the collStats command against the collection
859 "mycoll" in database "mydb".
860 #include <bson/bson.h>
862 #include <mongoc/mongoc.h>
863 #include <stdio.h>
864 int
866 main (int argc, char *argv[])
867 {
868 mongoc_client_t *client;
869 mongoc_collection_t *collection;
870 bson_error_t error;
871 bson_t *command;
872 bson_t reply;
873 char *str;
874 mongoc_init ();
876 client = mongoc_client_new (
878 "mongodb://localhost:27017/?appname=executing-example");
879 collection = mongoc_client_get_collection (client, "mydb", "mycoll");
880 command = BCON_NEW ("collStats", BCON_UTF8 ("mycoll"));
882 if (mongoc_collection_command_simple (
883 collection, command, NULL, &reply, &error)) {
884 str = bson_as_canonical_extended_json (&reply, NULL);
885 printf ("%s\n", str);
886 bson_free (str);
887 } else {
888 fprintf (stderr, "Failed to run command: %s\n", error.message);
889 }
890 bson_destroy (command);
892 bson_destroy (&reply);
893 mongoc_collection_destroy (collection);
894 mongoc_client_destroy (client);
895 mongoc_cleanup ();
896 return 0;
898 }
899 Compile the code and run it:
901 $ gcc -o executing executing.c $(pkg-config --cflags --libs libmongoc-1.0)
903 $ ./executing
904 { "ns" : "mydb.mycoll", "count" : 1, "size" : 48, "avgObjSize" : 48, "numExtents" : 1, "storageSize" : 8192,
905 "lastExtentSize" : 8192.000000, "paddingFactor" : 1.000000, "userFlags" : 1, "capped" : false, "nindexes" : 1,
906 "indexDetails" : { }, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1.000000 }
907 On Windows:
909 C:\> cl.exe /IC:\mongo-c-driver\include\libbson-1.0 /IC:\mongo-c-driver\include\libmongoc-1.0 executing.c
911 C:\> executing
912 { "ns" : "mydb.mycoll", "count" : 1, "size" : 48, "avgObjSize" : 48, "numExtents" : 1, "storageSize" : 8192,
913 "lastExtentSize" : 8192.000000, "paddingFactor" : 1.000000, "userFlags" : 1, "capped" : false, "nindexes" : 1,
914 "indexDetails" : { }, "totalIndexSize" : 8176, "indexSizes" : { "_id_" : 8176 }, "ok" : 1.000000 }
915
917 The MongoDB C Driver is thread-unaware in the vast majority of its
918 operations. This means it is up to the programmer to guarantee
919 thread-safety.
920 However, mongoc_client_pool_t is thread-safe and is used to fetch a
922 mongoc_client_t in a thread-safe manner. After retrieving a client from
923 the pool, the client structure should be considered owned by the call‐
924 ing thread. When the thread is finished, the client should be placed
925 back into the pool.
926 example-pool.c
928 /* gcc example-pool.c -o example-pool $(pkg-config --cflags --libs
930 * libmongoc-1.0) */
931 /* ./example-pool [CONNECTION_STRING] */
933 #include <mongoc/mongoc.h>
935 #include <pthread.h>
936 #include <stdio.h>
937 static pthread_mutex_t mutex;
939 static bool in_shutdown = false;
940 static void *
942 worker (void *data)
943 {
944 mongoc_client_pool_t *pool = data;
945 mongoc_client_t *client;
946 bson_t ping = BSON_INITIALIZER;
947 bson_error_t error;
948 bool r;
949 BSON_APPEND_INT32 (&ping, "ping", 1);
951 while (true) {
953 client = mongoc_client_pool_pop (pool);
954 /* Do something with client. If you are writing an HTTP server, you
955 * probably only want to hold onto the client for the portion of the
956 * request performing database queries.
957 */
958 r = mongoc_client_command_simple (
959 client, "admin", &ping, NULL, NULL, &error);
960 if (!r) {
962 fprintf (stderr, "%s\n", error.message);
963 }
964 mongoc_client_pool_push (pool, client);
966 pthread_mutex_lock (&mutex);
968 if (in_shutdown || !r) {
969 pthread_mutex_unlock (&mutex);
970 break;
971 }
972 pthread_mutex_unlock (&mutex);
974 }
975 bson_destroy (&ping);
977 return NULL;
978 }
979 int
981 main (int argc, char *argv[])
982 {
983 const char *uri_string = "mongodb://127.0.0.1/?appname=pool-example";
984 mongoc_uri_t *uri;
985 bson_error_t error;
986 mongoc_client_pool_t *pool;
987 pthread_t threads[10];
988 unsigned i;
989 void *ret;
990 pthread_mutex_init (&mutex, NULL);
992 mongoc_init ();
993 if (argc > 1) {
995 uri_string = argv[1];
996 }
997 uri = mongoc_uri_new_with_error (uri_string, &error);
999 if (!uri) {
1000 fprintf (stderr,
1001 "failed to parse URI: %s\n"
1002 "error message: %s\n",
1003 uri_string,
1004 error.message);
1005 return EXIT_FAILURE;
1006 }
1007 pool = mongoc_client_pool_new (uri);
1009 mongoc_client_pool_set_error_api (pool, 2);
1010 for (i = 0; i < 10; i++) {
1012 pthread_create (&threads[i], NULL, worker, pool);
1013 }
1014 sleep (10);
1016 pthread_mutex_lock (&mutex);
1017 in_shutdown = true;
1018 pthread_mutex_unlock (&mutex);
1019 for (i = 0; i < 10; i++) {
1021 pthread_join (threads[i], &ret);
1022 }
1023 mongoc_client_pool_destroy (pool);
1025 mongoc_uri_destroy (uri);
1026 mongoc_cleanup ();
1028 return EXIT_SUCCESS;
1030 }
1031
1034 To find information on advanced topics, browse the rest of the C driver
1035 guide or the official MongoDB documentation.
1036 For help with common issues, consult the Troubleshooting page. To
1038 report a bug or request a new feature, follow these instructions.
1039
1041 MongoDB, Inc
1042
1044 2017-present, MongoDB, Inc
10451.17.4 Feb 04, 2021 MONGOC_TUTORIAL(3)