WCF Data Service 的.NET Client 的不支持原生类型服务操作的解决方法

WCF Data Service  的.NET Client 的不支持返回值为原生类型（string,int)的服务操作调用，例如我们用如下服务操作：

[WebGet] 
public ObjectQuery<string> GetList(string entitySet, string propertyName)
{ 
               return this.CurrentDataSource.CreateQuery<string>(string.Format("SELECT VALUE E.{1} FROM MyEntities.{0} AS E", entitySet, propertyName)).Distinct(); 
}

通过下面的方法调用

MyEntities.CreateQuery<string>("GetList").AddQueryOption("entitySet","'Test'")
.AddQueryOption("propertyName","'Test'").BeginExecute(....);

会发生错误：

Error processing response stream. The XML element contains mixed content.    at System.Data.Services.Client.MaterializeAtom.ReadElementString(Boolean checkNullAttribute)    at System.Data.Services.Client.MaterializeAtom.ReadNext(ClientType currentType, Type expectedType, AtomParseState atom, EntityStates& entityState, Object& currentValue)    at System.Data.Services.Client.MaterializeAtom.MoveNext()    at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)    at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)

解决方法：

使用HttpWebRequest请求Rest服务，服务会返回类似下面的ATOM格式数据，通过Linq to XML进行操作：

<ServiceOpName xmlns="http://schemas.microsoft.com/ado/2007/08/dataservices"> 
<element xml:space="preserve">Value   </element>
...
</ServiceOpName> 
var q = MyEntities.CreateQuery<string>("GetList").AddQueryOption("entitySet","'Test'")
.AddQueryOption("propertyName","'Test'")；

WebClient wc = new WebClient();
wc.DownloadStringAsync(new Uri(q.ToString())); wc.DownloadStringCompleted += (s, e) =>
{ 
       XDocument xdoc = XDocument.Parse(e.Result); 
       List<string> list = xdoc.Root.Descendants(((XNamespace)@"http://schemas.microsoft.com/ado/2007/08/dataservices") + "element")
       .Select(xe => xe.Value).ToList();
};