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學藝不精，陸續踩了幾次雷，整理DataContract與DataMember對序列化的影響備忘。

WCF預設使用DataContractSerializer執行序列化，而DataContractSerializer可依物件類別標註的[DataContract]及[DataMember]、[IgnoreDataMember]等Attribute決定哪些屬性該序列化。依照MSDN文件，DataContractSerializer的處理原則為：

  1. 類別標示[DataContract]時，只序列化有標示[DataMember]的項目
    註：DataMember不限於public Property，可用於各種存取層級（public、private、internal、protected）的Property或Field。
  2. 若類別未標示[DataContract]，DataContractSerializer預設會序列化「所有可讀寫的public Property及Field」，此時可透過[IgnoreDataMember]負向表列不要序列化的Property或Field。

我設計了以下幾個型別來觀察DataContractSerializer行為，有Property有Field，有public有private，再配合[DataContract]、[DataMember]、[IgnoreDataMember]組合出不同變化：

using System.Runtime.Serialization;
 
[DataContract]
public class Blah1
{
    public int PropNoAttr { get; set; }
    public int Field;
    private int PrivProp { get; set; }
    private int PrivField;
 
}
 
[DataContract]
public class Blah2
{
    public int PropNoAttr { get; set; }
    [DataMember]
    public int PropAttr { get; set; }
    public int Field;
    [DataMember]
    private int PrivProp { get; set; }
    [DataMember]
    private int PrivField;
 
}
 
[DataContract]
public class Blah3
{
    public int PropNoAttr { get; set; }
    [IgnoreDataMember]
    public int PropIgnoreAttr { get; set; }
    public int Field;
    private int PrivProp { get; set; }
    private int PrivField;
 
}
 
 
public class Blah4
{
    public int PropNoAttr { get; set; }
    [DataMember]
    public int PropAttr { get; set; }
    [IgnoreDataMember]
    public int PropIgnoreAttr { get; set; }
 
    public int Field;
    private int PrivProp { get; set; }
    private int PrivField;
}
 
public class Blah5
{
    public int PropNoAttr { get; set; }
    public int ReadonlyProp { get; }
    public int Field;
    private int PrivProp { get; set; }
    private int PrivField;
}

測試程式很簡單，用DataContractSerializer將Blah1到Blah5序列化成XML，Console.WriteLine出來，借用XDocument將XML以縮排格式輸出。

using System;
using System.IO;
using System.Runtime.Serialization;
using System.Text;
using System.Xml.Linq;
 
namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine(Serialize<Blah1>(new Blah1()));
            Console.WriteLine(Serialize<Blah2>(new Blah2()));
            Console.WriteLine(Serialize<Blah3>(new Blah3()));
            Console.WriteLine(Serialize<Blah4>(new Blah4()));
            Console.WriteLine(Serialize<Blah5>(new Blah5()));
            Console.Read();
        }
        static string Serialize<T>(T graph)
        {
            DataContractSerializer dcs = new DataContractSerializer(typeof(T));
            MemoryStream ms = new MemoryStream();
            dcs.WriteObject(ms, graph);
            XDocument xd = XDocument.Parse(Encoding.UTF8.GetString(ms.ToArray()));
            return
                typeof(T).ToString() +
                "\n=====================================\n" +
                xd.ToString() + "\n";
        }
    }
}

執行結果如下：

Blah1
=====================================
<Blah1 xmlns="http://schemas.datacontract.org/2004/07/" 
  xmlns:i="http://www.w3.org/2001/XMLSchema-instance" />
 
Blah2
=====================================
<Blah2 xmlns="http://schemas.datacontract.org/2004/07/" 
  xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
  <PrivField>0</PrivField>
  <PrivProp>0</PrivProp>
  <PropAttr>0</PropAttr>
</Blah2>
 
Blah3
=====================================
<Blah3 xmlns="http://schemas.datacontract.org/2004/07/" 
  xmlns:i="http://www.w3.org/2001/XMLSchema-instance" />
 
Blah4
=====================================
<Blah4 xmlns="http://schemas.datacontract.org/2004/07/" 
  xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
  <Field>0</Field>
  <PropAttr>0</PropAttr>
  <PropNoAttr>0</PropNoAttr>
</Blah4>
 
Blah5
=====================================
<Blah5 xmlns="http://schemas.datacontract.org/2004/07/" 
  xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
  <Field>0</Field>
  <PropNoAttr>0</PropNoAttr>
</Blah5>
  1. Blah1
    只標了[DataContract]沒標任何[DataMember]，XML空空如也，沒有任何Property或Field被序列化
  2. Blah2
    標註[DataContract]後，所有標註[DataMember]的成員都包含在XML中，不論public或private，不管是Property或是Field
  3. Blah3
    標註[DataContract]後DataContractSerializer只認[DataMember]辦事，[IgnoreDataMember]沒有作用，XML是空的
  4. Blah4
    未標註[DataContract]，除了[IgnoreDataMember] PropIgnoreAttr外，所有public的Property及Field都被序列化
  5. Blah5
    未加任何Attribute，DataContractSerializer將序列化所有公開Property及Field，但Property限定可讀寫者，刻意放了一個public ReadonlyProp { get; }唯讀屬性，果然被排除了。

實驗驗證完畢！


Comments

# by Jonh doe

最後一個blah4 應該是blah5

# by Jeffrey

to John, 一如往例，沒有錯字就不是黑大真跡 orz orz orz。謝謝指正。

# by Carter

Property 似乎不能用 readonly

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