包含投影不起作用

Question

我有这个查询

    var test = context.Assignments
        .Include(a => a.Customer)
        .Include(a => a.Subscriptions)
        .Select(a => new AssignmentWithSubscriptionCount { SubscriptionCount = a.Subscriptions.Count(), Assignment = a })
        .ToList();

    var name = test.First().Assignment.Customer.Name;

它无法急切地加载客户，我在 stackoverflow 上看到了类似的问题，看起来你不能将投影与 include 一起使用。但我还没有找到解决我的问题的方法..有人吗？

编辑：这是一个可以工作的投影的急切负载，它比上面的示例更复杂，所以我一生都无法理解出了什么问题，谢谢。

    var test = context.PublicationStateGroups
        .Include(p => p.PublicationStates.Select(ps => ps.AllowedPublicationStateActions.Select(aps => aps.PublicationStateAction)))
        .Select(psg => new StateAndGroupInfo
        {
            ShowReport = psg.PublicationStates.Any(p => p.PublicationStateReportTypeId.HasValue),
            Actions = psg.PublicationStates.SelectMany(state => state.AllowedPublicationStateActions)
                .Select(a => a.PublicationStateAction)
                .Distinct()
        }).ToList();

    var eagerTest = test.First().Actions.First().Name;

Answer 1

这是设计。 Include 不适用于具有投影或自定义联接的场景。

Answer 2

将客户添加到您的投影中：

var test = context.Assignments
    .Select(a => new AssignmentWithSubscriptionCount
    {
        SubscriptionCount = a.Subscriptions.Count(),
        Assignment = a,
        Customer = a.Customer
    });

var name = test.First().Customer.Name;

EF 上下文可能会确保自动填充 Assignment.Customer。

编辑

如果您不想或无法更改AssignmentWithSubscriptionCount类，您还可以投影到匿名类型，然后将内存中的结果复制到此类中：

var test = context.Assignments
    .Select(a => new
    {
        SubscriptionCount = a.Subscriptions.Count(),
        Assignment = a,
        Customer = a.Customer
    });

test.ToList() // executes query
    .Select(o =>
    {
        o.Assignment.Customer = o.Customer;
        return new AssignmentWithSubscriptionCount
        {
            SubscriptionCount = o.SubscriptionCount,
            Assignment = o.Assignment
        }
    });

另一种选择是显式加载（但每个加载的Assignment需要一次额外的往返）。