Provided by: libmongoc-doc_1.9.2+dfsg-1build1_all 
NAME
mongoc_guides - Guides
COMMON TASKS
Drivers for some other languages provide helper functions to perform certain common tasks. In the C
Driver we must explicitly build commands to send to the server.
This snippet contains example code for the explain, copydb and cloneCollection commands.
Setup
First we'll write some code to insert sample data: doc-common-insert.c.INDENT 0.0
/* Don't try to compile this file on its own. It's meant to be #included
by example code */
/* Insert some sample data */
bool
insert_data (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
enum N { ndocs = 4 };
bson_t *docs[ndocs];
bson_error_t error;
int i = 0;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]");
docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]");
docs[2] = BCON_NEW (
"x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]");
docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]");
for (i = 0; i < ndocs; i++) {
mongoc_bulk_operation_insert (bulk, docs[i]);
bson_destroy (docs[i]);
docs[i] = NULL;
}
ret = mongoc_bulk_operation_execute (bulk, NULL, &error);
if (!ret) {
fprintf (stderr, "Error inserting data: %s\n", error.message);
}
mongoc_bulk_operation_destroy (bulk);
return ret;
}
/* A helper which we'll use a lot later on */
void
print_res (const bson_t *reply)
{
BSON_ASSERT (reply);
char *str = bson_as_canonical_extended_json (reply, NULL);
printf ("%s\n", str);
bson_free (str);
}
explain Command
This is how to use the explain command in MongoDB 3.2+: explain.c.INDENT 0.0
bool
explain (mongoc_collection_t *collection)
{
bson_t *command;
bson_t reply;
bson_error_t error;
bool res;
command = BCON_NEW ("explain",
"{",
"find",
BCON_UTF8 (COLLECTION_NAME),
"filter",
"{",
"x",
BCON_INT32 (1),
"}",
"}");
res = mongoc_collection_command_simple (
collection, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "Error with explain: %s\n", error.message);
goto cleanup;
}
/* Do something with the reply */
print_res (&reply);
cleanup:
bson_destroy (&reply);
bson_destroy (command);
return res;
}
copydb Command
This example requires two instances of mongo to be running.
Here's how to use the copydb command to copy a database from another instance of MongoDB: copydb.c.INDENT
0.0
bool
copydb (mongoc_client_t *client, const char *other_host_and_port)
{
mongoc_database_t *admindb;
bson_t *command;
bson_t reply;
bson_error_t error;
bool res;
BSON_ASSERT (other_host_and_port);
/* Must do this from the admin db */
admindb = mongoc_client_get_database (client, "admin");
command = BCON_NEW ("copydb",
BCON_INT32 (1),
"fromdb",
BCON_UTF8 ("test"),
"todb",
BCON_UTF8 ("test2"),
/* If you want from a different host */
"fromhost",
BCON_UTF8 (other_host_and_port));
res =
mongoc_database_command_simple (admindb, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "Error with copydb: %s\n", error.message);
goto cleanup;
}
/* Do something with the reply */
print_res (&reply);
cleanup:
bson_destroy (&reply);
bson_destroy (command);
mongoc_database_destroy (admindb);
return res;
}
cloneCollection Command
This example requires two instances of mongo to be running.
Here's an example of the cloneCollection command to clone a collection from another instance of MongoDB:
clone-collection.c.INDENT 0.0
bool
clone_collection (mongoc_database_t *database, const char *other_host_and_port)
{
bson_t *command;
bson_t reply;
bson_error_t error;
bool res;
BSON_ASSERT (other_host_and_port);
command = BCON_NEW ("cloneCollection",
BCON_UTF8 ("test.remoteThings"),
"from",
BCON_UTF8 (other_host_and_port),
"query",
"{",
"x",
BCON_INT32 (1),
"}");
res =
mongoc_database_command_simple (database, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "Error with clone: %s\n", error.message);
goto cleanup;
}
/* Do something with the reply */
print_res (&reply);
cleanup:
bson_destroy (&reply);
bson_destroy (command);
return res;
}
Running the Examples
common-operations.c.INDENT 0.0
/*
* Copyright 2016 MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <mongoc.h>
#include <stdio.h>
const char *COLLECTION_NAME = "things";
#include "../doc-common-insert.c"
#include "explain.c"
#include "copydb.c"
#include "clone-collection.c"
int
main (int argc, char *argv[])
{
mongoc_database_t *database = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
char *host_and_port;
int res = 0;
char *other_host_and_port = NULL;
if (argc < 2 || argc > 3) {
fprintf (stderr,
"usage: %s MONGOD-1-CONNECTION-STRING "
"[MONGOD-2-HOST-NAME:MONGOD-2-PORT]\n",
argv[0]);
fprintf (stderr,
"MONGOD-1-CONNECTION-STRING can be "
"of the following forms:\n");
fprintf (stderr, "localhost\t\t\t\tlocal machine\n");
fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n");
fprintf (stderr,
"mongodb://user:pass@localhost:27017\t"
"local machine on port 27017, and authenticate with username "
"user and password pass\n");
return 1;
}
mongoc_init ();
if (strncmp (argv[1], "mongodb://", 10) == 0) {
host_and_port = bson_strdup (argv[1]);
} else {
host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]);
}
other_host_and_port = argc > 2 ? argv[2] : NULL;
client = mongoc_client_new (host_and_port);
if (!client) {
fprintf (stderr, "Invalid hostname or port: %s\n", host_and_port);
res = 2;
goto cleanup;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "test");
collection = mongoc_database_get_collection (database, COLLECTION_NAME);
printf ("Inserting data\n");
if (!insert_data (collection)) {
res = 3;
goto cleanup;
}
printf ("explain\n");
if (!explain (collection)) {
res = 4;
goto cleanup;
}
if (other_host_and_port) {
printf ("copydb\n");
if (!copydb (client, other_host_and_port)) {
res = 5;
goto cleanup;
}
printf ("clone collection\n");
if (!clone_collection (database, other_host_and_port)) {
res = 6;
goto cleanup;
}
}
cleanup:
if (collection) {
mongoc_collection_destroy (collection);
}
if (database) {
mongoc_database_destroy (database);
}
if (client) {
mongoc_client_destroy (client);
}
bson_free (host_and_port);
mongoc_cleanup ();
return res;
}
$ mongod
$ mkdir /tmp/db2$ mongod --dbpath /tmp/db2 --port 27018 # second instance
Now compile and run the example program:
$ cd examples/common_operations/$ gcc -Wall -o example common-operations.c $(pkg-config --cflags --libs libmongoc-1.0)$ ./example localhost:27017 localhost:27018
Inserting data
explain
{
"executionStats" : {
"allPlansExecution" : [],
"executionStages" : {
"advanced" : 19,
"direction" : "forward" ,
"docsExamined" : 76,
"executionTimeMillisEstimate" : 0,
"filter" : {
"x" : {
"$eq" : 1
}
},
"invalidates" : 0,
"isEOF" : 1,
"nReturned" : 19,
"needTime" : 58,
"needYield" : 0,
"restoreState" : 0,
"saveState" : 0,
"stage" : "COLLSCAN" ,
"works" : 78
},
"executionSuccess" : true,
"executionTimeMillis" : 0,
"nReturned" : 19,
"totalDocsExamined" : 76,
"totalKeysExamined" : 0
},
"ok" : 1,
"queryPlanner" : {
"indexFilterSet" : false,
"namespace" : "test.things",
"parsedQuery" : {
"x" : {
"$eq" : 1
}
},
"plannerVersion" : 1,
"rejectedPlans" : [],
"winningPlan" : {
"direction" : "forward" ,
"filter" : {
"x" : {
"$eq" : 1
}
},
"stage" : "COLLSCAN"
}
},
"serverInfo" : {
"gitVersion" : "05552b562c7a0b3143a729aaa0838e558dc49b25" ,
"host" : "MacBook-Pro-57.local",
"port" : 27017,
"version" : "3.2.6"
}
}
copydb
{ "ok" : 1 }
clone collection
{ "ok" : 1 }
ADVANCED CONNECTIONS
The following guide contains information specific to certain types of MongoDB configurations.
For an example of connecting to a simple standalone server, see the Tutorial. To establish a connection
with authentication options enabled, see the Authentication page.
Connecting to a Replica Set
Connecting to a replica set is much like connecting to a standalone MongoDB server. Simply specify the
replica set name using the ?replicaSet=myreplset URI option.
#include <bson.h>
#include <mongoc.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_init ();
/* Create our MongoDB Client */
client = mongoc_client_new (
"mongodb://host01:27017,host02:27017,host03:27017/?replicaSet=myreplset");
/* Do some work */
/* TODO */
/* Clean up */
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
TIP:
Multiple hostnames can be specified in the MongoDB connection string URI, with a comma separating
hosts in the seed list.
It is recommended to use a seed list of members of the replica set to allow the driver to connect to
any node.
Connecting to a Sharded Cluster
To connect to a sharded cluster, specify the mongos nodes the client should connect to. The C Driver will
automatically detect that it has connected to a mongos sharding server.
If more than one hostname is specified, a seed list will be created to attempt failover between the
mongos instances.
WARNING:
Specifying the replicaSet parameter when connecting to a mongos sharding server is invalid.
#include <bson.h>
#include <mongoc.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_init ();
/* Create our MongoDB Client */
client = mongoc_client_new ("mongodb://myshard01:27017/");
/* Do something with client ... */
/* Free the client */
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Connecting to an IPv6 Address
The MongoDB C Driver will automatically resolve IPv6 addresses from host names. However, to specify an
IPv6 address directly, wrap the address in [].
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://[::1]:27017");
Connecting to a UNIX Domain Socket
On UNIX-like systems, the C Driver can connect directly to a MongoDB server using a UNIX domain socket.
Pass the URL-encoded path to the socket, which must be suffixed with .sock. For example, to connect to a
domain socket at /tmp/mongodb-27017.sock:
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://%2Ftmp%2Fmongodb-27017.sock");
Include username and password like so:
mongoc_uri_t *uri = mongoc_uri_new ("mongodb://user:pass@%2Ftmp%2Fmongodb-27017.sock");
Connecting to a server over SSL
These are instructions for configuring TLS/SSL connections.
To run a server locally (on port 27017, for example):
$ mongod --port 27017 --sslMode requireSSL --sslPEMKeyFile server.pem --sslCAFile ca.pem
Add /?ssl=true to the end of a client URI.
mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?ssl=true");
MongoDB requires client certificates by default, unless the --sslAllowConnectionsWithoutCertificates is
provided. The C Driver can be configured to present a client certificate using a mongoc_ssl_opt_t:
const mongoc_ssl_opt_t *ssl_default = mongoc_ssl_opt_get_default ();
mongoc_ssl_opt_t ssl_opts = { 0 };
/* optionally copy in a custom trust directory or file; otherwise the default is used. */
memcpy (&ssl_opts, ssl_default, sizeof ssl_opts);
ssl_opts.pem_file = "client.pem"
mongoc_client_set_ssl_opts (client, &ssl_opts);
The client certificate provided by pem_file must be issued by one of the server trusted Certificate
Authorities listed in --sslCAFile, or issued by a CA in the native certificate store on the server when
omitted.
To verify the server certificate against a specific CA, provide a PEM armored file with a CA certificate,
or concatenated list of CA certificates using the ca_file option, or c_rehash directory structure of CAs,
pointed to using the ca_dir option. When no ca_file or ca_dir is provided, the driver will use CAs
provided by the native platform certificate store.
See mongoc_ssl_opt_t for more information on the various SSL related options.
Compressing data to and from MongoDB
MongoDB 3.4 added Snappy compression support, and zlib compression in 3.6. To enable compression support
the client must be configured with which compressors to use:
mongoc_client_t *client = NULL;
client = mongoc_client_new ("mongodb://localhost:27017/?compressors=snappy,zlib");
The compressors option specifies the priority order of compressors the client wants to use. Messages are
compressed if the client and server share any compressors in common.
Note that the compressor used by the server might not be the same compressor as the client used. For
example, if the client uses the connection string compressors=zlib,snappy the client will use zlib
compression to send data (if possible), but the server might still reply using snappy, depending on how
the server was configured.
The driver must be built with zlib and/or snappy support to enable compression support, any unknown (or
not compiled in) compressor value will be ignored.
Additional Connection Options
The full list of connection options can be found in the mongoc_uri_t docs.
Certain socket/connection related options are not configurable:
─────────────────────────────────────────────────────────────────────────
Option Description Value
─────────────────────────────────────────────────────────────────────────
SO_KEEPALIVE TCP Keep Alive Enabled
─────────────────────────────────────────────────────────────────────────
TCP_KEEPIDLE How long a connection needs 300 seconds
to remain idle before TCP
starts sending keepalive
probes
─────────────────────────────────────────────────────────────────────────
TCP_KEEPINTVL The time in seconds between 10 seconds
TCP probes
─────────────────────────────────────────────────────────────────────────
TCP_KEEPCNT How many probes to send, 9 probes
without acknowledgement,
before dropping the
connection
─────────────────────────────────────────────────────────────────────────
TCP_NODELAY Send packets as soon as Enabled (no buffering)
possible or buffer small
packets (Nagle algorithm)
┌───────────────┬──────────────────────────────┬────────────────────────┐
│ │ │ │
CONNECTION POOLING │ │ │ │
--
CURSORS
Handling Cursor Failures
Cursors exist on a MongoDB server. However, the mongoc_cursor_t structure gives the local process a
handle to the cursor. It is possible for errors to occur on the server while iterating a cursor on the
client. Even a network partition may occur. This means that applications should be robust in handling
cursor failures.
While iterating cursors, you should check to see if an error has occurred. See the following example for
how to robustly check for errors.
static void
print_all_documents (mongoc_collection_t *collection)
{
mongoc_cursor_t *cursor;
const bson_t *doc;
bson_error_t error;
bson_t query = BSON_INITIALIZER;
char *str;
cursor = mongoc_collection_find_with_opts (collection, query, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Failed to iterate all documents: %s\n", error.message);
}
mongoc_cursor_destroy (cursor);
}
Destroying Server-Side Cursors
The MongoDB C driver will automatically destroy a server-side cursor when mongoc_cursor_destroy() is
called. Failure to call this function when done with a cursor will leak memory client side as well as
consume extra memory server side. If the cursor was configured to never timeout, it will become a memory
leak on the server.
Tailable Cursors
Tailable cursors are cursors that remain open even after they've returned a final result. This way, if
more documents are added to a collection (i.e., to the cursor's result set), then you can continue to
call mongoc_cursor_next() to retrieve those additional results.
Here's a complete test case that demonstrates the use of tailable cursors.
NOTE:
Tailable cursors are for capped collections only.
An example to tail the oplog from a replica set. mongoc-tail.c.INDENT 0.0
#include <bson.h>
#include <mongoc.h>
#include <stdio.h>
#include <stdlib.h>
#ifdef _WIN32
#define sleep(_n) Sleep ((_n) *1000)
#endif
static void
print_bson (const bson_t *b)
{
char *str;
str = bson_as_canonical_extended_json (b, NULL);
fprintf (stdout, "%s\n", str);
bson_free (str);
}
static mongoc_cursor_t *
query_collection (mongoc_collection_t *collection, uint32_t last_time)
{
mongoc_cursor_t *cursor;
bson_t query;
bson_t gt;
bson_t opts;
BSON_ASSERT (collection);
bson_init (&query);
BSON_APPEND_DOCUMENT_BEGIN (&query, "ts", >);
BSON_APPEND_TIMESTAMP (>, "$gt", last_time, 0);
bson_append_document_end (&query, >);
bson_init (&opts);
BSON_APPEND_BOOL (&opts, "tailable", true);
BSON_APPEND_BOOL (&opts, "awaitData", true);
cursor = mongoc_collection_find_with_opts (collection, &query, &opts, NULL);
bson_destroy (&query);
bson_destroy (&opts);
return cursor;
}
static void
tail_collection (mongoc_collection_t *collection)
{
mongoc_cursor_t *cursor;
uint32_t last_time;
const bson_t *doc;
bson_error_t error;
bson_iter_t iter;
BSON_ASSERT (collection);
last_time = (uint32_t) time (NULL);
while (true) {
cursor = query_collection (collection, last_time);
while (!mongoc_cursor_error (cursor, &error) &&
mongoc_cursor_more (cursor)) {
if (mongoc_cursor_next (cursor, &doc)) {
if (bson_iter_init_find (&iter, doc, "ts") &&
BSON_ITER_HOLDS_TIMESTAMP (&iter)) {
bson_iter_timestamp (&iter, &last_time, NULL);
}
print_bson (doc);
}
}
if (mongoc_cursor_error (cursor, &error)) {
if (error.domain == MONGOC_ERROR_SERVER) {
fprintf (stderr, "%s\n", error.message);
exit (1);
}
}
mongoc_cursor_destroy (cursor);
sleep (1);
}
}
int
main (int argc, char *argv[])
{
mongoc_collection_t *collection;
mongoc_client_t *client;
if (argc != 2) {
fprintf (stderr, "usage: %s MONGO_URI\n", argv[0]);
return EXIT_FAILURE;
}
mongoc_init ();
client = mongoc_client_new (argv[1]);
if (!client) {
fprintf (stderr, "Invalid URI: \"%s\"\n", argv[1]);
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "local", "oplog.rs");
tail_collection (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
return 0;
}
$ gcc -Wall -o mongoc-tail mongoc-tail.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./mongoc-tail mongodb://example.com/?replicaSet=myReplSet
{
"h" : -8458503739429355503,
"ns" : "test.test",
"o" : {
"_id" : {
"$oid" : "5372ab0a25164be923d10d50"
}
},
"op" : "i",
"ts" : {
"$timestamp" : {
"i" : 1,
"t" : 1400023818
}
},
"v" : 2
}
The line of output is a sample from performing db.test.insert({}) from the mongo shell on the replica
set.
See also mongoc_cursor_set_max_await_time_ms.
BULK WRITE OPERATIONS
This tutorial explains how to take advantage of MongoDB C driver bulk write operation features. Executing
write operations in batches reduces the number of network round trips, increasing write throughput.
Bulk Insert
First we need to fetch a bulk operation handle from the mongoc_collection_t.
mongoc_bulk_operation_t *bulk =
mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
We can now start inserting documents to the bulk operation. These will be buffered until we execute the
operation.
The bulk operation will coalesce insertions as a single batch for each consecutive call to
mongoc_bulk_operation_insert(). This creates a pipelined effect when possible.
To execute the bulk operation and receive the result we call mongoc_bulk_operation_execute().
bulk1.c.INDENT 0.0
#include <assert.h>
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk1 (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
int i;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
for (i = 0; i < 10000; i++) {
doc = BCON_NEW ("i", BCON_INT32 (i));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
}
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
fprintf (stderr, "Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk1-example");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk1 (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Example reply document:
{"nInserted" : 10000,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : []
"writeConcernErrors" : [] }
Mixed Bulk Write Operations
MongoDB C driver also supports executing mixed bulk write operations. A batch of insert, update, and
remove operations can be executed together using the bulk write operations API.
Ordered Bulk Write Operations
Ordered bulk write operations are batched and sent to the server in the order provided for serial
execution. The reply document describes the type and count of operations performed. bulk2.c.INDENT 0.0
#include <assert.h>
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk2 (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *query;
bson_t *doc;
bson_t *opts;
bson_t reply;
char *str;
bool ret;
int i;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
/* Remove everything */
query = bson_new ();
mongoc_bulk_operation_remove (bulk, query);
bson_destroy (query);
/* Add a few documents */
for (i = 1; i < 4; i++) {
doc = BCON_NEW ("_id", BCON_INT32 (i));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
}
/* {_id: 1} => {$set: {foo: "bar"}} */
query = BCON_NEW ("_id", BCON_INT32 (1));
doc = BCON_NEW ("$set", "{", "foo", BCON_UTF8 ("bar"), "}");
mongoc_bulk_operation_update_many_with_opts (bulk, query, doc, NULL, &error);
bson_destroy (query);
bson_destroy (doc);
/* {_id: 4} => {'$inc': {'j': 1}} (upsert) */
opts = BCON_NEW ("upsert", BCON_BOOL (true));
query = BCON_NEW ("_id", BCON_INT32 (4));
doc = BCON_NEW ("$inc", "{", "j", BCON_INT32 (1), "}");
mongoc_bulk_operation_update_many_with_opts (bulk, query, doc, opts, &error);
bson_destroy (query);
bson_destroy (doc);
bson_destroy (opts);
/* replace {j:1} with {j:2} */
query = BCON_NEW ("j", BCON_INT32 (1));
doc = BCON_NEW ("j", BCON_INT32 (2));
mongoc_bulk_operation_replace_one_with_opts (bulk, query, doc, NULL, &error);
bson_destroy (query);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk2-example");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk2 (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Example reply document:
{ "nInserted" : 3,
"nMatched" : 2,
"nModified" : 2,
"nRemoved" : 10000,
"nUpserted" : 1,
"upserted" : [{"index" : 5, "_id" : 4}],
"writeErrors" : []
"writeConcernErrors" : [] }
The index field in the upserted array is the 0-based index of the upsert operation; in this example, the
sixth operation of the overall bulk operation was an upsert, so its index is 5.
Unordered Bulk Write Operations
Unordered bulk write operations are batched and sent to the server in arbitrary order where they may be
executed in parallel. Any errors that occur are reported after all operations are attempted.
In the next example the first and third operations fail due to the unique constraint on _id. Since we are
doing unordered execution the second and fourth operations succeed. bulk3.c.INDENT 0.0
#include <assert.h>
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk3 (mongoc_collection_t *collection)
{
bson_t opts = BSON_INITIALIZER;
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *query;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
/* false indicates unordered */
BSON_APPEND_BOOL (&opts, "ordered", false);
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
bson_destroy (&opts);
/* Add a document */
doc = BCON_NEW ("_id", BCON_INT32 (1));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* remove {_id: 2} */
query = BCON_NEW ("_id", BCON_INT32 (2));
mongoc_bulk_operation_remove_one (bulk, query);
bson_destroy (query);
/* insert {_id: 3} */
doc = BCON_NEW ("_id", BCON_INT32 (3));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* replace {_id:4} {'i': 1} */
query = BCON_NEW ("_id", BCON_INT32 (4));
doc = BCON_NEW ("i", BCON_INT32 (1));
mongoc_bulk_operation_replace_one (bulk, query, doc, false);
bson_destroy (query);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
bson_destroy (&opts);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk3-example");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk3 (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Example reply document:
{ "nInserted" : 0,
"nMatched" : 1,
"nModified" : 1,
"nRemoved" : 1,
"nUpserted" : 0,
"writeErrors" : [
{ "index" : 0,
"code" : 11000,
"errmsg" : "E11000 duplicate key error index: test.test.$_id_ dup key: { : 1 }" },
{ "index" : 2,
"code" : 11000,
"errmsg" : "E11000 duplicate key error index: test.test.$_id_ dup key: { : 3 }" } ],
"writeConcernErrors" : [] }
Error: E11000 duplicate key error index: test.test.$_id_ dup key: { : 1 }
The bson_error_t domain is MONGOC_ERROR_COMMAND and its code is 11000.
Bulk Operation Bypassing Document Validation
This feature is only available when using MongoDB 3.2 and later.
By default bulk operations are validated against the schema, if any is defined. In certain cases however
it may be necessary to bypass the document validation. bulk5.c.INDENT 0.0
#include <assert.h>
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk5_fail (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
/* Two inserts */
doc = BCON_NEW ("_id", BCON_INT32 (31));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_INT32 (32));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* The above documents do not comply to the schema validation rules
* we created previously, so this will result in an error */
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
static void
bulk5_success (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
/* Allow this document to bypass document validation.
* NOTE: When authentication is enabled, the authenticated user must have
* either the "dbadmin" or "restore" roles to bypass document validation */
mongoc_bulk_operation_set_bypass_document_validation (bulk, true);
/* Two inserts */
doc = BCON_NEW ("_id", BCON_INT32 (31));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_INT32 (32));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
bson_t *options;
bson_error_t error;
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_database_t *database;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk5-example");
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "testasdf");
/* Create schema validator */
options = BCON_NEW (
"validator", "{", "number", "{", "$gte", BCON_INT32 (5), "}", "}");
collection =
mongoc_database_create_collection (database, "collname", options, &error);
if (collection) {
bulk5_fail (collection);
bulk5_success (collection);
mongoc_collection_destroy (collection);
} else {
fprintf (stderr, "Couldn't create collection: '%s'\n", error.message);
}
bson_free (options);
mongoc_database_destroy (database);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
{ "nInserted" : 0,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [
{ "index" : 0,
"code" : 121,
"errmsg" : "Document failed validation" } ] }
Error: Document failed validation
{ "nInserted" : 2,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [] }
The bson_error_t domain is MONGOC_ERROR_COMMAND.
Bulk Operation Write Concerns
By default bulk operations are executed with the write_concern of the collection they are executed
against. A custom write concern can be passed to the mongoc_collection_create_bulk_operation_with_opts()
method. Write concern errors (e.g. wtimeout) will be reported after all operations are attempted,
regardless of execution order. bulk4.c.INDENT 0.0
#include <assert.h>
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk4 (mongoc_collection_t *collection)
{
bson_t opts = BSON_INITIALIZER;
mongoc_write_concern_t *wc;
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t reply;
char *str;
bool ret;
wc = mongoc_write_concern_new ();
mongoc_write_concern_set_w (wc, 4);
mongoc_write_concern_set_wtimeout (wc, 100); /* milliseconds */
mongoc_write_concern_append (wc, &opts);
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
/* Two inserts */
doc = BCON_NEW ("_id", BCON_INT32 (10));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_INT32 (11));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
mongoc_write_concern_destroy (wc);
bson_destroy (&opts);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk4-example");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk4 (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
Example reply document and error message:
{ "nInserted" : 2,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [],
"writeConcernErrors" : [
{ "code" : 64,
"errmsg" : "waiting for replication timed out" }
] }
Error: waiting for replication timed out
The bson_error_t domain is MONGOC_ERROR_WRITE_CONCERN if there are write concern errors and no write
errors. Write errors indicate failed operations, so they take precedence over write concern errors, which
mean merely that the write concern is not satisfied yet.
Setting Collation Order
This feature is only available when using MongoDB 3.4 and later. bulk-collation.c.INDENT 0.0
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk_collation (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
bson_t *opts;
bson_t *doc;
bson_t *selector;
bson_t *update;
bson_error_t error;
bson_t reply;
char *str;
uint32_t ret;
/* insert {_id: "one"} and {_id: "One"} */
bulk = mongoc_collection_create_bulk_operation_with_opts (
collection, NULL);
doc = BCON_NEW ("_id", BCON_UTF8 ("one"));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
doc = BCON_NEW ("_id", BCON_UTF8 ("One"));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
/* "One" normally sorts before "one"; make "one" come first */
opts = BCON_NEW ("collation",
"{",
"locale",
BCON_UTF8 ("en_US"),
"caseFirst",
BCON_UTF8 ("lower"),
"}");
/* set x=1 on the document with _id "One", which now sorts after "one" */
update = BCON_NEW ("$set", "{", "x", BCON_INT64 (1), "}");
selector = BCON_NEW ("_id", "{", "$gt", BCON_UTF8 ("one"), "}");
mongoc_bulk_operation_update_one_with_opts (
bulk, selector, update, opts, &error);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
bson_destroy (update);
bson_destroy (selector);
bson_destroy (opts);
mongoc_bulk_operation_destroy (bulk);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk-collation");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "db", "collection");
bulk_collation (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
{ "nInserted" : 2,
"nMatched" : 1,
"nModified" : 1,
"nRemoved" : 0,
"nUpserted" : 0,
"writeErrors" : [ ]
}
Unacknowledged Bulk Writes
Set "w" to zero for an unacknowledged write. The driver sends unacknowledged writes using the legacy
opcodes OP_INSERT, OP_UPDATE, and OP_DELETE. bulk6.c.INDENT 0.0
#include <bcon.h>
#include <mongoc.h>
#include <stdio.h>
static void
bulk6 (mongoc_collection_t *collection)
{
bson_t opts = BSON_INITIALIZER;
mongoc_write_concern_t *wc;
mongoc_bulk_operation_t *bulk;
bson_error_t error;
bson_t *doc;
bson_t *selector;
bson_t reply;
char *str;
bool ret;
wc = mongoc_write_concern_new ();
mongoc_write_concern_set_w (wc, 0);
mongoc_write_concern_append (wc, &opts);
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, &opts);
doc = BCON_NEW ("_id", BCON_INT32 (10));
mongoc_bulk_operation_insert (bulk, doc);
bson_destroy (doc);
selector = BCON_NEW ("_id", BCON_INT32 (11));
mongoc_bulk_operation_remove_one (bulk, selector);
bson_destroy (selector);
ret = mongoc_bulk_operation_execute (bulk, &reply, &error);
str = bson_as_canonical_extended_json (&reply, NULL);
printf ("%s\n", str);
bson_free (str);
if (!ret) {
printf ("Error: %s\n", error.message);
}
bson_destroy (&reply);
mongoc_bulk_operation_destroy (bulk);
mongoc_write_concern_destroy (wc);
bson_destroy (&opts);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new ("mongodb://localhost/?appname=bulk6-example");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "test");
bulk6 (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
The reply document is empty:
{ }
Further Reading
See the Driver Bulk API Spec, which describes bulk write operations for all MongoDB drivers.
AGGREGATION FRAMEWORK EXAMPLES
This document provides a number of practical examples that display the capabilities of the aggregation
framework.
The Aggregations using the Zip Codes Data Set examples uses a publicly available data set of all zipcodes
and populations in the United States. These data are available at: zips.json.
Requirements
Let's check if everything is installed.
Use the following command to load zips.json data set into mongod instance:
$ mongoimport --drop -d test -c zipcodes zips.json
Let's use the MongoDB shell to verify that everything was imported successfully.
$ mongo test
MongoDB shell version: 2.6.1
connecting to: test
> db.zipcodes.count()
29467
> db.zipcodes.findOne()
{
"_id" : "35004",
"city" : "ACMAR",
"loc" : [
-86.51557,
33.584132
],
"pop" : 6055,
"state" : "AL"
}
Aggregations using the Zip Codes Data Set
Each document in this collection has the following form:
{
"_id" : "35004",
"city" : "Acmar",
"state" : "AL",
"pop" : 6055,
"loc" : [-86.51557, 33.584132]
}
In these documents:
• The _id field holds the zipcode as a string.
• The city field holds the city name.
• The state field holds the two letter state abbreviation.
• The pop field holds the population.
• The loc field holds the location as a [latitude, longitude] array.
States with Populations Over 10 Million
To get all states with a population greater than 10 million, use the following aggregation pipeline:
aggregation1.c.INDENT 0.0
#include <mongoc.h>
#include <stdio.h>
static void
print_pipeline (mongoc_collection_t *collection)
{
mongoc_cursor_t *cursor;
bson_error_t error;
const bson_t *doc;
bson_t *pipeline;
char *str;
pipeline = BCON_NEW ("pipeline",
"[",
"{",
"$group",
"{",
"_id",
"$state",
"total_pop",
"{",
"$sum",
"$pop",
"}",
"}",
"}",
"{",
"$match",
"{",
"total_pop",
"{",
"$gte",
BCON_INT32 (10000000),
"}",
"}",
"}",
"]");
cursor = mongoc_collection_aggregate (
collection, MONGOC_QUERY_NONE, pipeline, NULL, NULL);
while (mongoc_cursor_next (cursor, &doc)) {
str = bson_as_canonical_extended_json (doc, NULL);
printf ("%s\n", str);
bson_free (str);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "Cursor Failure: %s\n", error.message);
}
mongoc_cursor_destroy (cursor);
bson_destroy (pipeline);
}
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_collection_t *collection;
mongoc_init ();
client = mongoc_client_new (
"mongodb://localhost:27017?appname=aggregation-example");
mongoc_client_set_error_api (client, 2);
collection = mongoc_client_get_collection (client, "test", "zipcodes");
print_pipeline (collection);
mongoc_collection_destroy (collection);
mongoc_client_destroy (client);
mongoc_cleanup ();
return 0;
}
{ "_id" : "PA", "total_pop" : 11881643 }
{ "_id" : "OH", "total_pop" : 10847115 }
{ "_id" : "NY", "total_pop" : 17990455 }
{ "_id" : "FL", "total_pop" : 12937284 }
{ "_id" : "TX", "total_pop" : 16986510 }
{ "_id" : "IL", "total_pop" : 11430472 }
{ "_id" : "CA", "total_pop" : 29760021 }
The above aggregation pipeline is build from two pipeline operators: $group and $match.
The $group pipeline operator requires _id field where we specify grouping; remaining fields specify how
to generate composite value and must use one of the group aggregation functions: $addToSet, $first,
$last, $max, $min, $avg, $push, $sum. The $match pipeline operator syntax is the same as the read
operation query syntax.
The $group process reads all documents and for each state it creates a separate document, for example:
{ "_id" : "WA", "total_pop" : 4866692 }
The total_pop field uses the $sum aggregation function to sum the values of all pop fields in the source
documents.
Documents created by $group are piped to the $match pipeline operator. It returns the documents with the
value of total_pop field greater than or equal to 10 million.
Average City Population by State
To get the first three states with the greatest average population per city, use the following
aggregation:
pipeline = BCON_NEW ("pipeline", "[",
"{", "$group", "{", "_id", "{", "state", "$state", "city", "$city", "}", "pop", "{", "$sum", "$pop", "}", "}", "}",
"{", "$group", "{", "_id", "$_id.state", "avg_city_pop", "{", "$avg", "$pop", "}", "}", "}",
"{", "$sort", "{", "avg_city_pop", BCON_INT32 (-1), "}", "}",
"{", "$limit", BCON_INT32 (3) "}",
"]");
This aggregate pipeline produces:
{ "_id" : "DC", "avg_city_pop" : 303450.0 }
{ "_id" : "FL", "avg_city_pop" : 27942.29805615551 }
{ "_id" : "CA", "avg_city_pop" : 27735.341099720412 }
The above aggregation pipeline is build from three pipeline operators: $group, $sort and $limit.
The first $group operator creates the following documents:
{ "_id" : { "state" : "WY", "city" : "Smoot" }, "pop" : 414 }
Note, that the $group operator can't use nested documents except the _id field.
The second $group uses these documents to create the following documents:
{ "_id" : "FL", "avg_city_pop" : 27942.29805615551 }
These documents are sorted by the avg_city_pop field in descending order. Finally, the $limit pipeline
operator returns the first 3 documents from the sorted set.
DISTINCT AND MAPREDUCE
This document provides some practical, simple, examples to demonstrate the distinct and mapReduce
commands.
Setup
First we'll write some code to insert sample data: doc-common-insert.c.INDENT 0.0
/* Don't try to compile this file on its own. It's meant to be #included
by example code */
/* Insert some sample data */
bool
insert_data (mongoc_collection_t *collection)
{
mongoc_bulk_operation_t *bulk;
enum N { ndocs = 4 };
bson_t *docs[ndocs];
bson_error_t error;
int i = 0;
bool ret;
bulk = mongoc_collection_create_bulk_operation_with_opts (collection, NULL);
docs[0] = BCON_NEW ("x", BCON_DOUBLE (1.0), "tags", "[", "dog", "cat", "]");
docs[1] = BCON_NEW ("x", BCON_DOUBLE (2.0), "tags", "[", "cat", "]");
docs[2] = BCON_NEW (
"x", BCON_DOUBLE (2.0), "tags", "[", "mouse", "cat", "dog", "]");
docs[3] = BCON_NEW ("x", BCON_DOUBLE (3.0), "tags", "[", "]");
for (i = 0; i < ndocs; i++) {
mongoc_bulk_operation_insert (bulk, docs[i]);
bson_destroy (docs[i]);
docs[i] = NULL;
}
ret = mongoc_bulk_operation_execute (bulk, NULL, &error);
if (!ret) {
fprintf (stderr, "Error inserting data: %s\n", error.message);
}
mongoc_bulk_operation_destroy (bulk);
return ret;
}
/* A helper which we'll use a lot later on */
void
print_res (const bson_t *reply)
{
BSON_ASSERT (reply);
char *str = bson_as_canonical_extended_json (reply, NULL);
printf ("%s\n", str);
bson_free (str);
}
distinct command
This is how to use the distinct command to get the distinct values of x which are greater than 1:
distinct.c.INDENT 0.0
bool
distinct (mongoc_database_t *database)
{
bson_t *command;
bson_t reply;
bson_error_t error;
bool res;
bson_iter_t iter;
bson_iter_t array_iter;
double val;
command = BCON_NEW ("distinct",
BCON_UTF8 (COLLECTION_NAME),
"key",
BCON_UTF8 ("x"),
"query",
"{",
"x",
"{",
"$gt",
BCON_DOUBLE (1.0),
"}",
"}");
res =
mongoc_database_command_simple (database, command, NULL, &reply, &error);
if (!res) {
fprintf (stderr, "Error with distinct: %s\n", error.message);
goto cleanup;
}
/* Do something with reply (in this case iterate through the values) */
if (!(bson_iter_init_find (&iter, &reply, "values") &&
BSON_ITER_HOLDS_ARRAY (&iter) &&
bson_iter_recurse (&iter, &array_iter))) {
fprintf (stderr, "Couldn't extract \"values\" field from response\n");
goto cleanup;
}
while (bson_iter_next (&array_iter)) {
if (BSON_ITER_HOLDS_DOUBLE (&array_iter)) {
val = bson_iter_double (&array_iter);
printf ("Next double: %f\n", val);
}
}
cleanup:
/* cleanup */
bson_destroy (command);
bson_destroy (&reply);
return res;
}
mapReduce - basic example
A simple example using the map reduce framework. It simply adds up the number of occurrences of each
"tag".
First define the map and reduce functions: constants.c.INDENT 0.0
const char *const COLLECTION_NAME = "things";
/* Our map function just emits a single (key, 1) pair for each tag
in the array: */
const char *const MAPPER = "function () {"
"this.tags.forEach(function(z) {"
"emit(z, 1);"
"});"
"}";
/* The reduce function sums over all of the emitted values for a
given key: */
const char *const REDUCER = "function (key, values) {"
"var total = 0;"
"for (var i = 0; i < values.length; i++) {"
"total += values[i];"
"}"
"return total;"
"}";
/* Note We can't just return values.length as the reduce function
might be called iteratively on the results of other reduce
steps. */
Run the mapReduce command: map-reduce-basic.c.INDENT 0.0
bool
map_reduce_basic (mongoc_database_t *database)
{
bson_t reply;
bson_t *command;
bool res;
bson_error_t error;
mongoc_cursor_t *cursor;
const bson_t *doc;
bool map_reduce_done = false;
bool query_done = false;
const char *out_collection_name = "outCollection";
mongoc_collection_t *out_collection;
/* Empty find query */
bson_t find_query = BSON_INITIALIZER;
/* Construct the mapReduce command */
/* Other arguments can also be specified here, like "query" or
"limit" and so on */
command = BCON_NEW ("mapReduce",
BCON_UTF8 (COLLECTION_NAME),
"map",
BCON_CODE (MAPPER),
"reduce",
BCON_CODE (REDUCER),
"out",
BCON_UTF8 (out_collection_name));
res =
mongoc_database_command_simple (database, command, NULL, &reply, &error);
map_reduce_done = true;
if (!res) {
fprintf (stderr, "MapReduce failed: %s\n", error.message);
goto cleanup;
}
/* Do something with the reply (it doesn't contain the mapReduce results) */
print_res (&reply);
/* Now we'll query outCollection to see what the results are */
out_collection =
mongoc_database_get_collection (database, out_collection_name);
cursor = mongoc_collection_find_with_opts (
out_collection, &find_query, NULL, NULL);
query_done = true;
/* Do something with the results */
while (mongoc_cursor_next (cursor, &doc)) {
print_res (doc);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "ERROR: %s\n", error.message);
res = false;
goto cleanup;
}
cleanup:
/* cleanup */
if (query_done) {
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (out_collection);
}
if (map_reduce_done) {
bson_destroy (&reply);
bson_destroy (command);
}
return res;
}
mapReduce - more complicated example
You must have replica set running for this.
In this example we contact a secondary in the replica set and do an "inline" map reduce, so the results
are returned immediately: map-reduce-advanced.c.INDENT 0.0
bool
map_reduce_advanced (mongoc_database_t *database)
{
bson_t *command;
bson_error_t error;
bool res = true;
mongoc_cursor_t *cursor;
mongoc_read_prefs_t *read_pref;
const bson_t *doc;
/* Construct the mapReduce command */
/* Other arguments can also be specified here, like "query" or "limit"
and so on */
/* Read the results inline from a secondary replica */
command = BCON_NEW ("mapReduce",
BCON_UTF8 (COLLECTION_NAME),
"map",
BCON_CODE (MAPPER),
"reduce",
BCON_CODE (REDUCER),
"out",
"{",
"inline",
"1",
"}");
read_pref = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
cursor = mongoc_database_command (
database, MONGOC_QUERY_NONE, 0, 0, 0, command, NULL, read_pref);
/* Do something with the results */
while (mongoc_cursor_next (cursor, &doc)) {
print_res (doc);
}
if (mongoc_cursor_error (cursor, &error)) {
fprintf (stderr, "ERROR: %s\n", error.message);
res = false;
}
mongoc_cursor_destroy (cursor);
mongoc_read_prefs_destroy (read_pref);
bson_destroy (command);
return res;
}
Running the Examples
Here's how to run the example code basic-aggregation.c.INDENT 0.0
/*
* Copyright 2016 MongoDB, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <mongoc.h>
#include <stdio.h>
#include "constants.c"
#include "../doc-common-insert.c"
#include "distinct.c"
#include "map-reduce-basic.c"
#include "map-reduce-advanced.c"
int
main (int argc, char *argv[])
{
mongoc_database_t *database = NULL;
mongoc_client_t *client = NULL;
mongoc_collection_t *collection = NULL;
char *host_and_port = NULL;
int res = 0;
if (argc != 2) {
fprintf (stderr, "usage: %s CONNECTION-STRING\n", argv[0]);
fprintf (stderr,
"the connection string can be of the following forms:\n");
fprintf (stderr, "localhost\t\t\t\tlocal machine\n");
fprintf (stderr, "localhost:27018\t\t\t\tlocal machine on port 27018\n");
fprintf (stderr,
"mongodb://user:pass@localhost:27017\t"
"local machine on port 27017, and authenticate with username "
"user and password pass\n");
return 1;
}
mongoc_init ();
if (strncmp (argv[1], "mongodb://", 10) == 0) {
host_and_port = bson_strdup (argv[1]);
} else {
host_and_port = bson_strdup_printf ("mongodb://%s", argv[1]);
}
client = mongoc_client_new (host_and_port);
if (!client) {
fprintf (stderr, "Invalid hostname or port: %s\n", host_and_port);
res = 2;
goto cleanup;
}
mongoc_client_set_error_api (client, 2);
database = mongoc_client_get_database (client, "test");
collection = mongoc_database_get_collection (database, COLLECTION_NAME);
printf ("Inserting data\n");
if (!insert_data (collection)) {
res = 3;
goto cleanup;
}
printf ("distinct\n");
if (!distinct (database)) {
res = 4;
goto cleanup;
}
printf ("map reduce\n");
if (!map_reduce_basic (database)) {
res = 5;
goto cleanup;
}
printf ("more complicated map reduce\n");
if (!map_reduce_advanced (database)) {
res = 6;
goto cleanup;
}
cleanup:
if (collection) {
mongoc_collection_destroy (collection);
}
if (database) {
mongoc_database_destroy (database);
}
if (client) {
mongoc_client_destroy (client);
}
if (host_and_port) {
bson_free (host_and_port);
}
mongoc_cleanup ();
return res;
}
to do this can be found here).
$ mongod
Now compile and run the example program:
$ cd examples/basic_aggregation/
$ gcc -Wall -o agg-example basic-aggregation.c $(pkg-config --cflags --libs libmongoc-1.0)
$ ./agg-example localhost
Inserting data
distinct
Next double: 2.000000
Next double: 3.000000
map reduce
{ "result" : "outCollection", "timeMillis" : 155, "counts" : { "input" : 84, "emit" : 126, "reduce" : 3, "output" : 3 }, "ok" : 1 }
{ "_id" : "cat", "value" : 63 }
{ "_id" : "dog", "value" : 42 }
{ "_id" : "mouse", "value" : 21 }
more complicated map reduce
{ "results" : [ { "_id" : "cat", "value" : 63 }, { "_id" : "dog", "value" : 42 }, { "_id" : "mouse", "value" : 21 } ], "timeMillis" : 14, "counts" : { "input" : 84, "emit" : 126, "reduce" : 3, "output" : 3 }, "ok" : 1 }
USING LIBMONGOC IN A MICROSOFT VISUAL STUDIO PROJECT
Download and install libmongoc on your system, then open Visual Studio, select "File→New→Project...", and
create a new Win32 Console Application. [image]
Remember to switch the platform from 32-bit to 64-bit: [image]
Right-click on your console application in the Solution Explorer and select "Properties". Choose to edit
properties for "All Configurations", expand the "C/C++" options and choose "General". Add to the
"Additional Include Directories" these paths:
C:\mongo-c-driver\include\libbson-1.0
C:\mongo-c-driver\include\libmongoc-1.0
[image]
(If you chose a different CMAKE_INSTALL_PREFIX when you ran CMake, your include paths will be different.)
Also in the Properties dialog, expand the "Linker" options and choose "Input", and add to the "Additional
Dependencies" these libraries:
C:\mongo-c-driver\lib\bson-1.0.lib
C:\mongo-c-driver\lib\mongoc-1.0.lib
[image]
Adding these libraries as dependencies provides linker symbols to build your application, but to actually
run it, libbson's and libmongoc's DLLs must be in your executable path. Select "Debugging" in the
Properties dialog, and set the "Environment" option to:
PATH=c:/mongo-c-driver/bin
[image]
Finally, include "mongoc.h" in your project's "stdafx.h":
#include <mongoc.h>
Static linking
Following the instructions above, you have dynamically linked your application to the libbson and
libmongoc DLLs. This is usually the right choice. If you want to link statically instead, update your
"Additional Dependencies" list by removing bson-1.0.lib and mongoc-1.0.lib and replacing them with these
libraries:
C:\mongo-c-driver\lib\bson-static-1.0.lib
C:\mongo-c-driver\lib\mongoc-static-1.0.lib
ws2_32.lib
Secur32.lib
Crypt32.lib
BCrypt.lib
[image]
(To explain the purpose of each library: bson-static-1.0.lib and mongoc-static-1.0.lib are static
archives of the driver code. The socket library ws2_32 is required by libbson, which uses the socket
routine gethostname to help guarantee ObjectId uniqueness. The BCrypt library is used by libmongoc for
SSL connections to MongoDB, and Secur32 and Crypt32 are required for enterprise authentication methods
like Kerberos.)
Finally, define two preprocessor symbols before including mongoc.h in your stdafx.h:
#define BSON_STATIC
#define MONGOC_STATIC
#include <mongoc.h>
Making these changes to your project is only required for static linking; for most people, the
dynamic-linking instructions above are preferred.
Next Steps
Now you can build and debug applications in Visual Studio that use libbson and libmongoc. Proceed to
making-a-connection in the tutorial to learn how connect to MongoDB and perform operations.
CREATING INDEXES
To create indexes on a MongoDB collection, execute the createIndexes command with
mongoc_database_write_command_with_opts. See the MongoDB Manual entry for the createIndexes command for
details.
Example
example-create-indexes.c.INDENT 0.0
/* gcc example-create-indexes.c -o example-create-indexes $(pkg-config --cflags
* --libs libmongoc-1.0) */
/* ./example-create-indexes [CONNECTION_STRING [COLLECTION_NAME]] */
#include <mongoc.h>
#include <stdio.h>
#include <stdlib.h>
int
main (int argc, char *argv[])
{
mongoc_client_t *client;
mongoc_database_t *db;
const char *uristr = "mongodb://127.0.0.1/?appname=create-indexes-example";
const char *collection_name = "test";
bson_t keys;
char *index_name;
bson_t *create_indexes;
bson_t reply;
char *reply_str;
bson_error_t error;
bool r;
mongoc_init ();
if (argc > 1) {
uristr = argv[1];
}
if (argc > 2) {
collection_name = argv[2];
}
client = mongoc_client_new (uristr);
if (!client) {
fprintf (stderr, "Failed to parse URI.\n");
return EXIT_FAILURE;
}
mongoc_client_set_error_api (client, 2);
db = mongoc_client_get_database (client, "test");
/* ascending index on field "x" */
bson_init (&keys);
BSON_APPEND_INT32 (&keys, "x", 1);
index_name = mongoc_collection_keys_to_index_string (&keys);
create_indexes = BCON_NEW ("createIndexes",
BCON_UTF8 (collection_name),
"indexes",
"[",
"{",
"key",
BCON_DOCUMENT (&keys),
"name",
BCON_UTF8 (index_name),
"}",
"]");
r = mongoc_database_write_command_with_opts (
db, create_indexes, NULL /* opts */, &reply, &error);
reply_str = bson_as_json (&reply, NULL);
printf ("%s\n", reply_str);
if (!r) {
fprintf (stderr, "Error in createIndexes: %s\n", error.message);
}
bson_free (index_name);
bson_free (reply_str);
bson_destroy (&reply);
bson_destroy (create_indexes);
mongoc_database_destroy (db);
mongoc_client_destroy (client);
mongoc_cleanup ();
return r ? EXIT_SUCCESS : EXIT_FAILURE;
}
AUTHOR
MongoDB, Inc
COPYRIGHT
2018, MongoDB, Inc
1.9.3-dev Feb 05, 2018 MONGOC_GUIDES(3)