Question

我无法弄清楚如何完成这个LINQ查询。我有一个像这样的数据库：

User  ->  UserAccess  <-  Terminal  <-  Site

终端属于站点，UserAccess指定哪些用户可以访问哪些终端。对于给定用户，我想按站点检索所有可用的终端。鉴于Site已经维护了Terminals的集合，这将是Site[]，但只填充了Terminals的子集。

我从（我认为）错误的结尾开始，我能够检索Sites的列表，并过滤孩子Terminals：

using (MsSqlDataContextDataContext db = new MsSqlDataContextDataContext()) { // This is part of a WCF Data Service. If I don't LoadWith I have lazy-loading problems DataLoadOptions options = new DataLoadOptions(); options.LoadWith<site>(s => s.Terminals); // I found AssociateWith can filter on a child collection, but I can't work out // how to do the same for grand-child. options.AssociateWith<site>(s => s.Terminals.Where(t => t.Active)); db.LoadOptions = options; return db.sites.Where(s => s.Active).ToArray(); }

但我无法通过子集合Terminals过滤UserAccess。

我决定再次尝试从中间查询，我想我已经接近了。我现在可以检索Terminals的列表，但我无法检索Sites的列表：

return db.UserAccess.Where(a => a.Username.Equals(username) && a.HasAccess )) .Select(a => a.Terminal).ToArray();

我尝试添加.GroupBy(t => t.Site)，但是当我真的希望我的现有类型填充这些结果时，会创建一个匿名类型。当我试图返回IGrouping<Site, Terminal>时，WCF也有了一些错误。

我觉得，如果我自己设法解决了一个解决方案，它将是11个链式命令，当有一种方法可以在2中完成时，它会让人们畏缩看到它。

Linq query to return grandparent, parent and grandchild based on a grandchild's property的答案会为每个结果生成一个匿名类型，您可以获得数百个终端，每个终端都有一个单独的网站，没有分组。

问题Linq query to return filtered data是我想要做的，但是（像他一样）我想避免明确地迭代数据。

编辑： 尝试提供最小，完整且可验证的示例。不幸的是，这太可怕了。我正在尝试复制我现有的类结构，它们是LINQ to SQL模型。它生成循环引用（Terminal具有Site的外键，但Site具有Terminals的集合。

public void LinqQuery() { Site s1 = new Site { SiteName = "Site 1", Terminals = new List<Terminal>() }; Site s2 = new Site { SiteName = "Site 2", Terminals = new List<Terminal>() }; Terminal t1 = new Terminal { TerminalName = "Terminal 1:1", site = s1, AccessList = new List<UserAccess>() }; Terminal t2 = new Terminal { TerminalName = "Terminal 2:1", site = s1, AccessList = new List<UserAccess>() }; s1.Terminals.Add(t1); s1.Terminals.Add(t2); Terminal t3 = new Terminal { TerminalName = "Terminal 3:2", site = s2, AccessList = new List<UserAccess>() }; Terminal t4 = new Terminal { TerminalName = "Terminal 4:2", site = s2, AccessList = new List<UserAccess>() }; s2.Terminals.Add(t3); s2.Terminals.Add(t4); User u1 = new User { Name = "Ian" }; UserAccess ua1 = new UserAccess { user = u1, terminal = t1 }; t1.AccessList.Add(ua1); UserAccess ua2 = new UserAccess { user = u1, terminal = t2 }; t2.AccessList.Add(ua2); UserAccess ua3 = new UserAccess { user = u1, terminal = t4 }; t4.AccessList.Add(ua3); Site[] allSites = {s1, s2}; Terminal[] allTerminals = {t1, t2, t3, t4}; UserAccess[] allUserAccess = {ua1, ua2, ua3}; // This gives me a list of all terminals where user "Ian" has access (3 Terminals) var v = allUserAccess.Where(ua => ua.user.Name.Equals("Ian")).Select(ua => ua.terminal).ToArray(); // If I take it one step further and Select the site, I end up with an array of 3 sites (only 2 exist) var v2 = v.Select(t => t.site).ToArray(); // What I want is the allSites array but with the terminals filtered. } internal class Site { public string SiteName { get; set; } public List<Terminal> Terminals { get; set; } } internal class Terminal { public string TerminalName { get; set; } public Site site { get; set; } public List<UserAccess> AccessList { get; set; } } internal class UserAccess { public User user { get; set; } public Terminal terminal { get; set; } } internal class User { public string Name { get; set; } }

Answer 1

就像linked question中的兄弟@DeclanMcD一样，我不得不求助于显式过滤数据。我觉得这个解决方案可能会更清洁，但我仍然不喜欢它：

// What I want is the allSites array but with the terminals filtered.
List<Site> toReturn = new List<Site>(allSites);
foreach (Site s in toReturn)
{
    // Look through every Terminal
    // And check if they have any UserAccess that would allow access.
    // If no access (!t.AccessList.Any), remove this Terminal.
    s.Terminals.RemoveAll(t => !t.AccessList.Any(
        a => a.user.Name.Equals("Ian")));
}

// Also if I want empty Sites removed:
toReturn.RemoveAll(s => !s.Terminals.Any());

外部foreach可能是LINQ-ified，但后来我再也无法读取它了。

任何更好的答案都会获得投票和赞赏。

LINQ根据孙子标准

1 个答案: