无法创建“Sunlight.Silverlight.Dcs.Web.PartsSupplier”类型的常量值。此上下文仅支持基元类型或枚举类型问题

今天写代码遇到一个问题，
            const string SCODE = "123";
            var suppliers = PartsSuppliers.Where(r => r.Code == SCODE).ToArray();
            var spares = from  spare in SpareParts
                         join partsSupplierRelation in PartsSupplierRelations on spare.Id equals partsSupplierRelation.PartId
                         join sup in suppliers on  partsSupplierRelation.SupplierId equals sup.Id
                         select spare;
            spares.Dump();

这样回报一个错误，无法创建“Sunlight.Silverlight.Dcs.Web.PartsSupplier”类型的常量值。此上下文仅支持基元类型或枚举类型问题

改成下面这样就好了

var spares = from sup in suppliers
                        join partsSupplierRelation in PartsSupplierRelations on sup.Id equals partsSupplierRelation.SupplierId
                        join spare in SpareParts on partsSupplierRelation.PartId equals spare.Id
                        select spare;
           spares.Dump();

不知道为什么，先记下来等有时间再去理解。