在ViewModel构造函数中初始化secondClass列表：

Public oneViewModel()
{
    SecondClassList = new List<SecondClass>();
)

记住从Linq查询中删除初始化。

编辑

List<oneViewModel> workOrderInfoList = (from abc in db.ABC
    join customer in db.Customers on abc.CustomerId equals customer.CustomerId into customers
    select new oneViewModel()
    {
        CustomerId = abc.CustomerId,
        OrderNumber = workOrderInfo.OrderNumber,
        OrderDate = abc.OrderDate,
        SecondClassList = abc.SecondClassList
    }).ToList();

编辑2

您的oneViewModel应该看起来像这样：

public class oneViewModel
{
    public oneViewModel
    {
        SecondClassList = new List<SecondClass>();
    }

    Public List<SecondClass> SecondClassList { get; set; }
}

linq查询应该如下所示：

List<oneViewModel> workOrderInfoList = (from abc in db.ABC
join customer in db.Customers on abc.CustomerId equals customer.CustomerId into customers
select new oneViewModel()
{
    CustomerId = abc.CustomerId,
    OrderNumber = workOrderInfo.OrderNumber,
    OrderDate = abc.OrderDate
}).ToList();

现在，您将拥有oneViewModel对象的列表。

你需要先执行query，然后初始化list，例如：

List<oneViewModel> workOrderInfoList = (from abc in db.ABC
  join customer in db.Customers on abc.CustomerId equals customer.CustomerId into customers).ToList()
  Select(n => new oneViewModel()
  {
     CustomerId = n.CustomerId,
     OrderNumber = workOrderInfo.OrderNumber,
     OrderDate = n.OrderDate,
     SecondClassList = new List<SecondClass>(),
  }).ToList();

显然，你不能像Linq to Entities那样创建一个空列表，但是你可以通过在列表中放入一个虚拟项，然后通过下面的Where子句过滤掉它来欺骗它。
可接受的解决方案对我的情况不起作用，因为我有一个更复杂的查询，其中oneViewModel在查询中被初始化了两次，一次是真实的数据，一次是空数据。错误：The type '{myType}' appears in two structurally incompatible initializations within a single LINQ to Entities query.我需要在查询中指定更多的列，而不是让构造函数在幕后完成。

List<oneViewModel> workOrderInfoList = (from abc in db.ABC
  join customer in db.Customers on abc.CustomerId equals customer.CustomerId into customers
  select new oneViewModel()
  {
     CustomerId = abc.CustomerId,
     OrderNumber = workOrderInfo.OrderNumber,
     OrderDate = abc.OrderDate,
     SecondClassList = new List<SecondClass>() { new SecondClass() }.Where(x => false).ToList(),
  }).ToList();