Question

我正在使用XmlDictionaryWriter将对象序列化为具有数据协定序列化程序的数据库。它的效果很好，大小和速度都比使用text / xml好2倍。

但是，我必须处理数据库中的大量记录，其中任何额外的字节都直接转换为数据库大小的千兆字节。这就是为什么我喜欢通过使用XML字典来进一步缩小尺寸。

我该怎么做？

我看到XmlDictionaryWriter.CreateBinaryWriter静态方法接受IXmlDictionary类型的第2个参数。 MSDN说“XmlDictionary用作共享字典”。

首先，我尝试使用系统提供的实现：

XmlDictionary dict = new XmlDictionary();
string[] dictEntries = new string[]
{
    "http://schemas.datacontract.org/2004/07/MyContracts",
    "http://www.w3.org/2001/XMLSchema-instance",
    "MyElementName1",
    "MyElementName2",
    "MyElementName3",
};
foreach ( string s in dictEntries )
        dict.Add( s );

结果是.NET框架完全忽略了字典，仍然将上述字符串作为纯文本插入，而不是仅仅引用相应的字典条目。

然后我创建了自己的IXmlDictionary实现：

class MyDictionary : IXmlDictionary
{
    Dictionary<int, string> values = new Dictionary<int, string>();
    Dictionary<string, int> keys = new Dictionary<string, int>();

    MyDictionary()
    {
        string[] dictEntries = new string[]
        {
            "http://schemas.datacontract.org/2004/07/MyContracts",
            "http://www.w3.org/2001/XMLSchema-instance",
            "MyElementName1",
            "MyElementName2",
            "MyElementName3",
        };

        foreach ( var s in dictEntries )
            this.Add( s );
    }

    static IXmlDictionary s_instance = new MyDictionary();
    public static IXmlDictionary instance { get { return s_instance; } }

    void Add( string val )
    {
        if ( keys.ContainsKey( val ) )
            return;
        int id = values.Count + 1;
        values.Add( id, val );
        keys.Add( val, id );
    }

    bool IXmlDictionary.TryLookup( XmlDictionaryString value, out XmlDictionaryString result )
    {
        if ( value.Dictionary == this )
        {
            result = value;
            return true;
        }
        return this.TryLookup( value.Value, out result );
    }

    bool IXmlDictionary.TryLookup( int key, out XmlDictionaryString result )
    {
        string res;
        if ( !values.TryGetValue( key, out res ) )
        {
            result = null;
            return false;
        }
        result = new XmlDictionaryString( this, res, key );
        return true;
    }

    public bool /* IXmlDictionary. */ TryLookup( string value, out XmlDictionaryString result )
    {
        int key;
        if ( !keys.TryGetValue( value, out key ) )
        {
            result = null;
            return false;
        }

        result = new XmlDictionaryString( this, value, key );
        return true;
    }
}

结果是 - 我的TryLookup方法被称为OK，但是DataContractSerializer.WriteObject会生成一个空文档。

如何使用预共享词典？

提前致谢！

P.S。我不想搞乱XmlBinaryReaderSession / XmlBinaryWriterSession：我没有“会话”，而是我有一个10 GB +数据库同时被许多线程访问。我想要的只是静态预定词典。

更新：好的我已经发现我只需要调用“XmlDictionaryWriter.Flush”。唯一剩下的问题是 - 为什么系统提供的IXmlDictionary实现不能按预期工作？

Answer 1

对于XmlDictionaryWriter，您需要使用会话 example：

   private static Stream SerializeBinaryWithDictionary(Person person,DataContractSerializer serializer)
    {
        var stream = new MemoryStream();
        var dictionary = new XmlDictionary();
        var session = new XmlBinaryWriterSession();
        var key = 0;
        session.TryAdd(dictionary.Add("FirstName"), out key);
        session.TryAdd(dictionary.Add("LastName"), out key);
        session.TryAdd(dictionary.Add("Birthday"), out key);
        session.TryAdd(dictionary.Add("Person"), out key);
        session.TryAdd(dictionary.Add("http://www.friseton.com/Name/2010/06"),out key);
        session.TryAdd(dictionary.Add("http://www.w3.org/2001/XMLSchema-instance"),out key);

        var writer = XmlDictionaryWriter.CreateBinaryWriter(stream, dictionary, session);
        serializer.WriteObject(writer, person);
        writer.Flush();
        return stream;
    }

Answer 2

我无法使用IXmlDictionary复制问题的唯一方法是我的课程没有使用DataContract属性修饰。以下应用程序显示装饰和未装饰类的大小差异。

using System;
using System.Runtime.Serialization;
using System.Xml;

namespace XmlPresharedDictionary
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Serialized sizes");
            Console.WriteLine("-------------------------");
            TestSerialization<MyXmlClassUndecorated>("Undecorated: ");
            TestSerialization<MyXmlClassDecorated>("Decorated:   ");
            Console.ReadLine();
        }

        private static void TestSerialization<T>(string lineComment) where T : new()
        {
            XmlDictionary xmlDict = new XmlDictionary();
            xmlDict.Add("MyElementName1");

            DataContractSerializer serializer = new DataContractSerializer(typeof(T));

            using (System.IO.MemoryStream stream = new System.IO.MemoryStream())
            using (var writer = XmlDictionaryWriter.CreateBinaryWriter(stream, xmlDict))
            {
                serializer.WriteObject(writer, new T());
                writer.Flush();
                Console.WriteLine(lineComment + stream.Length.ToString());
            }
        }
    }

    //[DataContract]
    public class MyXmlClassUndecorated
    {
        public MyElementName1[] MyElementName1 { get; set; }

        public MyXmlClassUndecorated()
        {
            MyElementName1 = new MyElementName1[] { new MyElementName1("A A A A A"), new MyElementName1("A A A A A") };
        }
    }

    [DataContract]
    public class MyXmlClassDecorated
    {
        public MyElementName1[] MyElementName1 { get; set; }

        public MyXmlClassDecorated()
        {
            MyElementName1 = new MyElementName1[] { new MyElementName1("A A A A A"), new MyElementName1("A A A A A") };
        }
    }

    [DataContract]
    public class MyElementName1
    {
        [DataMember]
        public string Value { get; set; }

        public MyElementName1(string value) { Value = value; }
    }
}

带有预共享字典的.NET二进制XML

2 个答案: