BSON ドキュメントの解析と反復処理

解析

BSON documents are lazily parsed as necessary. To begin parsing a BSON document, use one of the provided Libbson functions to create a new bson_t from existing data such as bson_new_from_data. This will make a copy of the data so that additional mutations may occur to the BSON document.

Tip

If you only want to parse a BSON document and have no need to mutate it, you may use bson_init_static to avoid making a copy of the data.

bson_t *b;
b = bson_new_from_data (my_data, my_data_len);
if (!b) {
   fprintf (stderr, "The specified length embedded in <my_data> did not match "
                    "<my_data_len>\n");
   return;
}
bson_destroy (b);

Only two checks are performed when creating a new bson_t from an existing buffer. First, the document must begin with the buffer length, matching what was expected by the caller. Second, the document must end with the expected trailing \0 byte.

To parse the document further we use a bson_iter_t to iterate the elements within the document. Let's print all of the field names in the document.

bson_t *b;
bson_iter_t iter;
if ((b = bson_new_from_data (my_data, my_data_len))) {
   if (bson_iter_init (&iter, b)) {
      while (bson_iter_next (&iter)) {
         printf ("Found element key: \"%s\"\n", bson_iter_key (&iter));
      }
   }
   bson_destroy (b);
}

Converting a document to JSON uses a bson_iter_t and bson_visitor_t to iterate all fields of a BSON document recursively and generate a UTF-8 encoded JSON string.

bson_t *b;
char *json;
if ((b = bson_new_from_data (my_data, my_data_len))) {
    if ((json = bson_as_canonical_extended_json (b, NULL))) {
       printf ("%s\n", json);
       bson_free (json);
    }
    bson_destroy (b);
}

サブドキュメントへの再帰

libbson は、サブドキュメントまたはサブ配列を詳しく説明するための便利なサブイテレータを提供します。以下は、「foo」という名前のサブドキュメントを調べて、そのフィールド名を出力する例です。

bson_iter_t iter;
bson_iter_t child;
char *json;
if (bson_iter_init_find (&iter, doc, "foo") &&
    BSON_ITER_HOLDS_DOCUMENT (&iter) && bson_iter_recurse (&iter, &child)) {
   while (bson_iter_next (&child)) {
      printf ("Found sub-key of \"foo\" named \"%s\"\n",
              bson_iter_key (&child));
   }
}

ドット表記を使用したフィールドの検索

Using the bson_iter_recurse function exemplified above, bson_iter_find_descendant can find a field for you using the MongoDB style path notation such as "foo.bar.0.baz".

{"foo": {"bar": [{"baz: 1}]}}のようなドキュメントを作成し、 "baz"フィールドを見つけます。

bson_t *b;
bson_iter_t iter;
bson_iter_t baz;
b =
   BCON_NEW ("foo", "{", "bar", "[", "{", "baz", BCON_INT32 (1), "}", "]", "}");
if (bson_iter_init (&iter, b) &&
    bson_iter_find_descendant (&iter, "foo.bar.0.baz", &baz) &&
    BSON_ITER_HOLDS_INT32 (&baz)) {
   printf ("baz = %d\n", bson_iter_int32 (&baz));
}
bson_destroy (b);

BSON ドキュメントの検証

If all you want to do is validate that a BSON document is valid, you can use bson_validate.

size_t err_offset;
if (!bson_validate (doc, BSON_VALIDATE_NONE, &err_offset)) {
   fprintf (stderr,
            "The document failed to validate at offset: %u\n",
            (unsigned) err_offset);
}

See the bson_validate documentation for more information and examples.

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