LINQ：填充NotMapped字段

Question

当我尝试填充NotMapped字段时，我有一个错误（“无法在LINQ to Entities查询中构造实体或复杂类型'MyTable'）。

这里有我的例子：我的代码中的错误是什么？ 并且，是否可以在不填充字段的情况下填充ExternalDescription？

public partial class MyTable
{
    public int MyTableId { get; set; }

    public int Table2Id { get; set; }

    public int Field1 { get; set; }
    public int Field2 { get; set; }

    [NotMapped]
    public String ExternalDescription { get; set; }
}

public partial class MyTable2
{
    public int MyTable2Id { get; set; }
    public String Description { get; set; }
}


var records = (from t1 in db.MyTable
                join t2 in db.MyTable2 on t1.Table2Id equals t2.MyTable2Id
                select new MyTable
                {
                    MyTableId = t1.MyTableId,
                    Table2Id = t1.Table2Id,
                    Field1 = t1.Field1,
                    Field2 = t1.Field2,
                    ExternalDescription = t2.Description
                }).ToList();