Question

我有树对象。

一个对象EFacebook，非常简单，有一个名为id的属性。

class EFacebook
{
   public string id { get; set; }
}

A EUser，更复杂。 EUser获取内部EProvider列表，每个EProvider获取一个类型。像：

class EUser
{
    public string name { get; set; }
    public List<EProvider> EProviders { get; set; }
}

class EProvider
{
   public enum EnumType
   {
      facebook = 1,
      twitter = 2
   }
   public string id { get; set; }
   public EnumType type { get; set; }
}

两个列表:(提供者列表，内部用户，是可选的，可以为空）：

// list of facebooks
List<EFacebook> facebooks = new List<EFacebook>();

facebooks.Add(new EFacebook { id = "1" });
facebooks.Add(new EFacebook { id = "2" });
facebooks.Add(new EFacebook { id = "3" });

// list of users
List<EUser> users = new List<EUser>();
List<EProvider> ps1 = new List<EProvider>();

ps1.Add(new EProvider { id = "1", type = EProvider.EnumType.facebook });
ps1.Add(new EProvider { id = "2", type = EProvider.EnumType.twitter });

List<EProvider> ps2 = new List<EProvider>();
ps2.Add(new EProvider { id = "3", type = EProvider.EnumType.facebook });
ps2.Add(new EProvider { id = "4", type = EProvider.EnumType.twitter });

EUser u1 = new EUser { name = "somea", EProviders = ps1 };
EUser u2 = new EUser { name = "someb", EProviders = ps2 };
EUser u3 = new EUser { name = "somec" };

users.Add(u1);
users.Add(u2);
users.Add(u3);

现在，我需要根据facebooks和facebook.id之间的关系获取两个user.eprovider(of enum facebook).id子列表。这意味着，EFacebook的列表仅包含facebook id 2的对象，因为我没有具有类型facebook和{{1}的提供者的用户2，以及包含id {1}}和{1}的对象的EFacebook列表，因为我的用户facebook类型为id和provider 1和facebook 3。

我尝试了很多，但它不起作用：

id

任何帮助将不胜感激。

Answer 1

怎么样：

// Create an enumerable of all IDs of Facebook providers from the users list
var facebookIds = users
    // Exclude all users with a null EProviders list
    .Where(u => u.EProviders != null)
    // For each user, select all EProviders with type == facebook
    // and use SelectMany to flatten them into a single enumerable
    .SelectMany(u => u.EProviders.Where(p => p.type == EProvider.EnumType.facebook));

// Use Join to find all facebooks whose IDs also exist in the facebookIds set constructed above
var facebooksWithUsers = facebooks.Join(facebookIds, f => f.id, p => p.id, (f, p) => f);

// Use Except to find the opposite subset
var facebooksWithoutUsers = facebooks.Except(facebooksWithUsers);

// Write the contents of the two sets to the console
Console.WriteLine("facebooksWithUsers:");
foreach (var fb in facebooksWithUsers)
{
    Console.WriteLine(fb.id);
}

Console.WriteLine();
Console.WriteLine("facebooksWithoutUsers:");
foreach (var fb in facebooksWithoutUsers)
{
    Console.WriteLine(fb.id);
}

输出：

facebooksWithUsers:
1
3

facebooksWithoutUsers:
2

linq查询语法，如何产生两个列表组合的标准

1 个答案: