求助silverlight+ado.net实体模型+域服务下如何用select选择器？
我想在查询时只返回想要的列，别把所有的列都返回，就是弄不明白怎么写。请问这应该怎么弄？

C# code

            AccountsDomainContext context = new AccountsDomainContext();            var query = from x in context.GetCompanysQuery()                        where x.CompanyName.Equals("北京")                        select x.CompanyId; //错误:无法将类型CompanyId隐式转换为Companys

C# code

            AccountsDomainContext context = new AccountsDomainContext();            context.Load(context.GetCompanysQuery().Select(x=>x.CompanyId) //同样的错误                , callback =>                {                    if (!callback.HasError)                    {                        dataGrid1.ItemsSource = callback.Entities;                    }                }, null);

XML code

[OperationContract]public Models.TMaster GetEntity(string masterKey){    using (Models.TestDataClassesDataContext db = new Models.TestDataClassesDataContext())    {        db.DeferredLoadingEnabled = false;        System.Data.Linq.DataLoadOptions option = new System.Data.Linq.DataLoadOptions();        option.LoadWith<Models.TMaster>(m => m.TDetail);        db.LoadOptions = option;        return db.TMaster.FirstOrDefault(m => m.MasterKey == masterKey);    }}