LINQ select items of List

Question

我将首先展示一些代码，然后我将尝试告诉您我想要什么。

Thread thread = db.Threads
            .AsNoTracking()
            .FirstOrDefault(x=>x.Name == name);

var threadTopics = db.Topics
            .AsNoTracking()
            .Where(x => x.ThreadId == thread.Id && x.PinType != PinType.Advertisement)
            .ToList();

thread.Topics = threadTopics;

基本上，我想我的主题，但我不需要所有的主题，我只需要“不广告”的主题。这对我来说很有效，但我觉得我可以用一个请求来做这件事，但我不知道怎么做。

我试过了，但它不起作用：

Thread thread = db.Threads
            .AsNoTracking()
            .Where(x=>x.Name == name)
            .Select(x=> new Thread
            {
                Topics = x.Topics.Select(x=>x.PinType != PinType.Advertisement)
            });

型号：

class Thread {
    int ThreadId {get;set;} 
    ICollection<Topic> Topics {get;set;}
}
class Topic {
    int TopicId {get;set;}  
    int ThreadId {get;set;}
    Thread Thread {get;set;}    
    PinType PinType {get;set;}
}

Answer 1

Thread thread = db.Threads
        .AsNoTracking()
        .Where(x=>x.Name == name)
        .Select(x=> new Thread
        {
            Topics = x.Topics.Select(x=>x.PinType != PinType.Advertisement)
        });

左边是线程，右边是IEnumberable。您还会错过new Thread中的Id。将其更改为：

var threads = db.Threads
        .AsNoTracking()
        .Where(x=>x.Name == name)
        .Select(x=> new Thread
        {
            ThreadId = x.ThreadId,
            Topics = x.Topics.Where(x=>x.PinType != PinType.Advertisement).ToList()
        });

也许你需要

Thread thread = threads.FirstOrDefault();

然后我们可以将其简化为

Thread thread = db.Threads
        .AsNoTracking()
        .Where(x=>x.Name == name)
        .Select(x=> new Thread
        {
            ThreadId = x.ThreadId,
            Topics = x.Topics.Where(x=>x.PinType != PinType.Advertisement).ToList()
        }).FirstOrDefault();

Answer 2

这一切都如我所愿。首先，我寻找我需要的线程，在我找到它之后，我删除了其中的一些主题。我想在一个请求中做到这一点，但我认为这也“没问题”。

Thread thread = db.Threads
            .AsNoTracking()
            .FirstOrDefault(x=>x.Name == name);

thread.Topics = thread.Topics.Where(x => x.PinType != PinType.Advertisement).ToList();