Question

可以通过100万种方式做到这一点。

Problem. I have a list of servers which belongs to a country.

各国有许多服务器,因此其导航有两种方式(我认为其名称是)

Now I have a list of servers with there country set and want to group by country so I can get the opposite list.

List of countries with all there servers attached to the ICollection of the Country ( Servers )

var groupBy = list.GroupBy(x => x.Country, x => x, (c, s) => new {c, s});
foreach (var country in groupBy)
{
}

This will almost give me the result I want, but now I have 2 anon types. C which is country and S which is the list of servers.

How can I attach the list of servers to the country object s Collection.

班级类似......简化。

public class Server
{
    public short SID { get; set; }
    public Country Country { get; set; }
}

public class Country
{
    public byte CID { get; set; }
    public ICollection<Server> Servers { get; set; }
}

我猜测,我们可以建立一个有信息的新国家,然后把服务器名单放在建筑商......但我认为这种超技能。

......这种奇迹很简单,但我在这里失去了。

Update

我需要选择所有满足某种条件的服务器。因此,我有一个国家服务器清单。现在我刚刚需要改变名单。能否以其他方式做到这一点?

I m using the Repository Pattern with EF 4 Code First. IRepository I only have the following methods available with a option to eager load a property: Single, SingleOrDefault, Find and FindAll

没有 la的负荷,他们都返回ICollection或一个T。

Answer 1

它像你真的想要建立从国家到服务器的眼光:

var lookup = servers.ToLookup(server => server.Country);

If that s not what you re looking for, please let me know how it doesn t do what you want :)

诚然,没有保证每个<代码>的国家都将在原始清单中拥有所有服务器,而这种区别确实是问题。

If your Server already has the Country set, can you not assume that the data is already consistent? If not, shouldn t your Server really have a CID instead of a Country reference? Having a property which will sometimes be consistent with "this" object and sometimes not (i.e. whether server.Country.Contains(server) is guaranteed to return true or not) is ugly IMO.

EDIT:Okae, 一种可能的nic子替代物是:

var query = servers.GroupBy(server => server.Country.CID);
                   .Select(g => new Country { CID = g.Key,
                                              Servers = g.ToList() });

This is almost the same as fermaref s approach, but I m explicitly using Country.CID to avoid two servers with equivalent countries not ending up in the same bucket due to potentially odd equality rules.

Answer 2

现在,我有一份列有每个国家的服务器清单,希望按国家分类,这样我就可以确定相反的清单。

Linq is for querying and it has a functional mindset where you generate new instances instead of modifying existing instances.

如果你想改变这种情况,则先令:

List<Server> servers = GetServers();

foreach(Server server in servers)
{
  Country c = server.Country;
  c.Servers.Add(server);
}

如果你必须使用林克:

List<Server> servers = GetServers();

foreach(IGrouping<Country, Server> g in servers.GroupBy(s => s.Country))
{
  Country c = g.Key;
  c.Servers = g.ToList();
}

现在我刚刚需要改变名单。

ILookup<Country, Server> lookup = servers.ToLookup(s => s.Country);
List<Country> countries = lookup.Select(g => g.Key).ToList();
foreach(Country c in countries)
{
  c.Servers = lookup[c].ToList();
}
return countries;

Answer 3

如果您能保证每个<代码>的国家的物体已经包含所有服务器,则您可创建新的<代码>。国家目标:

var groupBy = list.GroupBy(
                    x => x.Country, 
                    x => x, (c, s) => 
                                new Country 
                                {
                                  CID = c.CID, 
                                  Servers =  s.ToList()});

然而,我不相信这符合你们的意愿。

If you can guarantee that the Country object will always contain all Servers, you can could use the following:

var countries = list.SelectMany(s => s.Country).Distinct();

或者,如果您的<代码>,则 does 执行<条码>

var groupBy = list.GroupBy(x => x.Country).Select(x => x.Key);

Update

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