bson_error_t error;
bson_t *doc = bson_new();
bson_t child;
bson_append_document_begin(doc, "$set", -1, &child);
BSON_APPEND_INT64(&child, "field1", 22);
bson_append_document_end(doc, &child);

bson_t query;
bson_init(&query);
BSON_APPEND_INT64(&query, "id", 1);

bool r = mongoc_collection_update(m_pCollection,
    MONGOC_UPDATE_NONE,
    &query,
    doc,
    NULL,
    &error);
if (!r)
{
    cout << "Update Failure: " << error.message;
}
bson_destroy(&query);
bson_destroy(doc);