附加到序列化集合

Question

我有某种类型的序列化数组。 有没有办法将新对象附加到这个序列化数组（以序列化形式）而不需要将已经保存的集合读入内存？

例子：

我有一个 file.xml，包含 10^12 个元素的 XML 序列化的实体数组。我需要在序列化文件中添加另外 10^5 个元素，但我不想读取所有以前的元素，追加新元素并将新数组写入流，因为它会占用大量资源（尤其是内存） .

如果它需要二进制序列化器，我不会有任何问题。

Answer 1

一般的解决方案是更改 XML 字节，这样您就不必像反序列化那样读取所有字节。

一般的步骤是：

1. 列表项
2. 打开文件流
3. 存储数组的结束节点
4. 序列化新项目
5. 将序列化字节写入流
6. 写结束节点

例如将整数添加到序列化数组的代码：

// Serialize array - in you case it the stream you read from file.xml
var ints = new[] { 1, 2, 3 };
var arraySerializer = new XmlSerializer(typeof(int[]));
var memoryStream = new MemoryStream(); // File.OpenWrite("file.xml")
arraySerializer.Serialize(new StreamWriter(memoryStream), ints);

// Save the closing node
int sizeOfClosingNode = 13; // In this case: "</ArrayOfInt>".Length
                            // Change the size to fit your array
                            // e.g. ("</ArrayOfOtherType>".Length)

// Set the location just before the closing tag
memoryStream.Position = memoryStream.Length - sizeOfClosingNode;

// Store the closing tag bytes
var buffer = new byte[sizeOfClosingNode];
memoryStream.Read(buffer, 0, sizeOfClosingNode);

// Set back to location just before the closing tag.
// In this location the new item will be written.
memoryStream.Position = memoryStream.Length - sizeOfClosingNode;

// Add to serialized array an item
var itemBuilder = new StringBuilder();
// Write the serialized item as string to itemBuilder
new XmlSerializer(typeof(int)).Serialize(new StringWriter(itemBuilder), 4);
// Get the serialized item XML element (strip the XML document declaration)
XElement newXmlItem = XElement.Parse(itemBuilder.ToString());
// Convert the XML to bytes can be written to the file
byte[] bytes = Encoding.Default.GetBytes(newXmlItem.ToString());
// Write new item to file.
memoryStream.Write(bytes, 0, bytes.Length);
// Write the closing tag.
memoryStream.Write(buffer, 0, sizeOfClosingNode);

// Example that it works
memoryStream.Position = 0;
var modifiedArray = (int[]) arraySerializer.Deserialize(memoryStream);
CollectionAssert.AreEqual(new[] { 1, 2, 3, 4 }, modifiedArray);