Updating a Document

The Basics

The following code example creates a new mongoc_client_t that we will use to communicate with MongoDB. The Connection String URI component is quite comprehensive.

Using our mongoc_client_t, we get a handle to a mongoc_collection_t which represents the remote collection. We create a new document, initialized with an _id and a field named hello and insert it into the test.test collection. Then, using that same _id, we update the document, overwriting an existing field and adding a new field.

Lastly, we release all of our heap allocated structures.

<file>example4.c</file> Update a document from the collection.


#include 
#include 
#include 

int
main (int   argc,
      char *argv[])
{
    mongoc_collection_t *collection;
    mongoc_client_t *client;
    bson_error_t error;
    bson_oid_t oid;
    bson_t *doc = NULL;
    bson_t *update = NULL;
    bson_t *query = NULL;

    mongoc_init ();

    client = mongoc_client_new ("mongodb://localhost:27017/");
    collection = mongoc_client_get_collection (client, "test", "test");

    bson_oid_init (&oid, NULL);
    doc = BCON_NEW ("_id", BCON_OID (&oid),
                    "hello", BCON_UTF8 ("world!"));

    if (!mongoc_collection_insert (collection, MONGOC_INSERT_NONE, doc, NULL, &error)) {
        printf ("%s\n", error.message);
        goto fail;
    }

    query = BCON_NEW ("_id", BCON_OID (&oid));
    update = BCON_NEW ("$set", "{",
                           "hello", BCON_UTF8 ("Everybody!"),
                           "updated", BCON_BOOL (true),
                       "}");

    if (!mongoc_collection_update (collection, MONGOC_UPDATE_NONE, query, update, NULL, &error)) {
        printf ("%s\n", error.message);
        goto fail;
    }

fail:
    if (doc)
        bson_destroy (doc);
    if (query)
        bson_destroy (query);
    if (update)
        bson_destroy (update);

    mongoc_collection_destroy (collection);
    mongoc_client_destroy (client);

    return 0;
}
]]>

Let's use GCC and pkg-config to compile example4.c.

gcc -o example4 example4.c $(pkg-config --cflags --libs libmongoc-1.0)

When using the MongoDB C Driver, you must call mongoc_init() at the beginning of your application. This allows the driver to initialize it's required subsystems. Failure to do so will result in a runtime crash.

Now let's run it!

./example4

Let's make a query with the MongoDB shell now and see what happened!

[christian@starpulse ~]$ mongo MongoDB shell version: 2.4.10 connecting to: test > use test switched to db test > db.test.find({}) { "_id" : { "$oid" : "534cde1a4f05ea4055d4cd4c" }, "hello" : "Everybody!", "updated" : true } > bye