包含投影不起作用

问题描述

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;

它急于加载客户，我在stackoverflow上看到类似的问题，它看起来像你不能使用包含的投影。但我还没有找到解决问题的方法..任何人？

It failes to eagerly load Customer, I've seen similar problems here on stackoverflow and it looks like you cant use projections with include. But I have not found a solution to my problem.. Anyone?

编辑：这是一个有投影的急切负载，它比上面的例子更复杂，所以我我的生活无法理解什么是错的，谢谢。

edit: Here is a eager load with projection that work, its more complex than the example above so I cant for my life understand whats wrong, thanks.

    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;

推荐答案

将客户添加到您的预测中：

Add the customer to your projection:

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 Assignment.Customer 自动填充。

The EF context will probably ensure that Assignment.Customer gets populated automatically.

编辑

如果您不想要或者无法更改 AssignmentWithSubscriptionCount 类，您也可以投影到匿名类型，然后将结果在内存中复制到此类中：

If you don't want or can't change the AssignmentWithSubscriptionCount class you can also project into an anonymous type and then copy the result in memory into this class:

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
        }
    });

另一种选择是明确加载（每次加载需要一次额外的往返分配虽然）。

Another option is explicite loading (requires one additional roundtrip per loaded Assignment though).

这篇关于包含投影不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！