Question

我最近在工作中遇到了一个问题，以下是源代码，

this.NameList = new ObservableCollection<Name>();

        List<Others> others1 = new List<Others>();
        others1.Add(new Others() { Company = "Company1", School = "School1" });
        others1.Add(new Others() { Company = "Company1", School = "School1" });
        others1.Add(new Others() { Company = "Company1", School = "School1" });

        List<Others> others2 = new List<Others>();
        others2.Add(new Others() { Company = "Company2", School = "School2" });
        others2.Add(new Others() { Company = "Company2", School = "School2" });
        others2.Add(new Others() { Company = "Company2", School = "School2" });

        List<Others> others3 = new List<Others>();
        others3.Add(new Others() { Company = "Company3", School = "School3" });
        others3.Add(new Others() { Company = "Company3", School = "School3" });
        others3.Add(new Others() { Company = "Company3", School = "School3" });

        this.NameList.Add(new Name() { FirstName = "Jacob", LastName = "Deng", Others = others1 });
        this.NameList.Add(new Name() { FirstName = "David", LastName = "Xu", Others = others2 });
        this.NameList.Add(new Name() { FirstName = "Helen", LastName = "Liu", Others = others3 });

please click here to see the output of above code

然后请阅读以下代码，

  List<Others> others1 = new List<Others>();
        others1.Add(new Others() { Company = "Company1", School = "School1" });
        others1.Add(new Others() { Company = "Company1", School = "School1" });
        others1.Add(new Others() { Company = "Company1", School = "School1" });

        List<Others> others2 = new List<Others>(); 
        List<Others> others3 = new List<Others>();

        this.NameList.Add(new Name() { FirstName = "Jacob", LastName = "Deng", Others = others1 });
        this.NameList.Add(new Name() { FirstName = "David", LastName = "Xu", Others = others2 });
        this.NameList.Add(new Name() { FirstName = "Helen", LastName = "Liu", Others = others3 });

Please click here for the output of the second snippet code

从上面的两个片段中，您可能会注意到第二个片段不包含other2和other3中的任何项目，您可以从预览输出中轻松理解。

现在问题来了，我们如何使用LINQ来IEnumerable来处理这种情况，如何使用LINQ从Others实体中删除那些项目？但我们需要保持other2和other3不为null（保持计数为0）。除了LINQ，还有其他解决方案吗？

我尝试使用以下内容，但失败了，

var others = ((MyVM)DataContext).NameList.Select(n => n.Others.Where(o => o.School == "School1")).ToList();

我刚做了一些测试，如果我们不使用LINQ，那么我们可以使用以下代码片段来修复它。

ObservableCollection<Name> nameList = ((MyVM)DataContext).NameList;
        foreach(Name n in nameList)
        {
            List<Others> removeList = new List<Others>();
            for(int i=0;i<n.Others.Count;i++)
            {
                if(n.Others[i].School!="School1")
                {
                    removeList.Add(n.Others[i]);
                }
            }
            foreach(Others other in removeList)
            {
                n.Others.Remove(other);
            }
        }

但它看起来非常冗余，我们知道LINQ非常有用，我相信它可以用LINQ修复。希望有人可以帮我修复LINQ，谢谢。

感谢有人可以帮助我。非常感谢。

Answer 1

在您的案例中使用List<T>.RemoveAll会更好。有关详细信息，请参阅Using LINQ to remove elements from a List<T>。

ObservableCollection<Name> nameList = ((MyVM)DataContext).NameList;
foreach(Name n in nameList)
{
    n.Others.RemoveAll(s => s.School != "School1");
}

Linq擅长只读迭代而不是更新/删除。如果你坚持使用Linq，你必须重新构建每个项目。

var newList =   from nl in this.namelist
                // this list can be empty but never null
                let notSchool1 = (from s in nl.Others
                                  where s.School != "School1"
                                  select s).ToList()
                select new Name 
                { 
                    FirstName = nl.FirstName,
                    LastName = nl.LastName,
                    Others = noSchool1
                };
this.NameList = new ObservableCollection<Name>(newList);

以上代码可能会破坏您应用中的其他功能，因为这些项目被观察。

Answer 2

据我了解你的问题，你想删除那些学校价值不高的学校1＆＃39;。有不同的方法，但我建议过滤你想要的NameList数据。

您可以尝试使用下面的代码来获取其他人列表＆＃39; School1＆＃39;

var result = NameList.Select(name => new Name()
            {
                FirstName = name.FirstName,
                LastName = name.LastName,
                Others = name.Others.Where(obj => obj.School == "School1").ToList()
            }
            ).ToList();

LINQ处理IEnumerable并从子实体中删除不匹配的项目

2 个答案: