Linq查询数据服务中使用的.NET匿名类型在选择时出错

当我编写一个相当简单的Linq查询客户端时，我看到了一个错误，该客户端应该根据我在这里读到的关于类似问题的其他问题来工作

我有以下测试代码：

var result = publicCtx.Participants.Where(x => x.CompanyID == 1008)
  .Select(x => new { ID = x.ID, Sequence = x.Sequence } ).ToList();

执行此代码时，会出现以下错误：

Construction of entity type instances must use object initializer with default constructor.

从我所读到的内容来看，需要无参数构造函数的标准解决方案是使用匿名类型，我在这里使用匿名类型。数据类型是int？用于CompanyID和Sequence，字符串用于ID。所有这些都是实体模型中可为空的字段（旧数据库仍在转换中）。我正在使用一个WCF数据服务，该服务使用npgsql数据提供程序来提供服务端的实体模型

当我创建一个基本类来返回结果时，一切都会成功：

public class ParticipantResult
{
    public string ID;
    public int? Sequence;
}

与

---

编辑：我添加了周围的代码以供参考：

public MainWindow()
{
    InitializeComponent();

    try
    {
        publicCtx = ContextProvider.Public();

        // This first Linq call DOES work with its anonymous type
        var plan = publicCtx.Companies.Where(x => x.ID == 1008).Select(x => new { x.ID, x.PlanID }).FirstOrDefault().PlanID;
        // This throws the error
        var participants = publicCtx.Participants.Where(x => x.PlanID == plan).Select(x => new { ID = x.ID, Sequence = x.Sequence } ).ToList();
        ...
    }
    catch(Exception e)
    {
        Console.Write(e.Message);
    }

    DataContext = this;
    NotifyAll(); // just a quick and dirty PropertyChanged call
}

public static class ContextProvider
{
    public static PublicContext Public()
    {
        var pub = new Public.PublicContext(new Uri(ConfigurationManager.ConnectionStrings["PublicConnection"].ConnectionString));
        pub.SendingRequest2 += AuthenticateContext;
        return pub;
    }

    private static void AuthenticateContext(object sender, System.Data.Services.Client.SendingRequest2EventArgs e)
    {
        var user = ConfigurationManager.AppSettings["Username"];
        var pw = ConfigurationManager.AppSettings["Password"];
        var encodeStr = user + ":" + pw;
        var encoded = Convert.ToBase64String(Encoding.ASCII.GetBytes(encodeStr));

        e.RequestMessage.SetHeader("Authorization", "Basic " + encoded);
    }
}

---

我还需要做些什么才能使匿名类型正常工作，这样我就不需要创建类来只为查询结果选择几列？

我不知道第一个代码段如何抛出报告的错误。你能展示完整的方法吗？在我看来，在这段代码之前或之后发生了更多的事情。我已经添加了周围的代码以进行澄清。谢谢

public MainWindow()
{
    InitializeComponent();

    try
    {
        publicCtx = ContextProvider.Public();

        // This first Linq call DOES work with its anonymous type
        var plan = publicCtx.Companies.Where(x => x.ID == 1008).Select(x => new { x.ID, x.PlanID }).FirstOrDefault().PlanID;
        // This throws the error
        var participants = publicCtx.Participants.Where(x => x.PlanID == plan).Select(x => new { ID = x.ID, Sequence = x.Sequence } ).ToList();
        ...
    }
    catch(Exception e)
    {
        Console.Write(e.Message);
    }

    DataContext = this;
    NotifyAll(); // just a quick and dirty PropertyChanged call
}

public static class ContextProvider
{
    public static PublicContext Public()
    {
        var pub = new Public.PublicContext(new Uri(ConfigurationManager.ConnectionStrings["PublicConnection"].ConnectionString));
        pub.SendingRequest2 += AuthenticateContext;
        return pub;
    }

    private static void AuthenticateContext(object sender, System.Data.Services.Client.SendingRequest2EventArgs e)
    {
        var user = ConfigurationManager.AppSettings["Username"];
        var pw = ConfigurationManager.AppSettings["Password"];
        var encodeStr = user + ":" + pw;
        var encoded = Convert.ToBase64String(Encoding.ASCII.GetBytes(encodeStr));

        e.RequestMessage.SetHeader("Authorization", "Basic " + encoded);
    }
}