C＃中的多列LINQ中的多个列组

Question

请注意： 我已经看到在堆栈溢出中有很多像这样的问题。但他们不适合我，因为我的情况稍有不同。因此，请不要将其标记为重复，直到正确阅读整个问题并理解我想要的场景。

我有一类像如下：

public class ActualClass 
    { 
     public string BookName { get; set; } 
     public string IssuerName { get; set; } 
     public DateTime DateOfIssue { get; set; } 
     public bool Status { get; set; } 
    } 

它具有以下表中的数据：以下

我想将它们按发行者名称和DateOfIssue viewModel等级：

public class ViewModel 
    { 
     public string IssuerName { get; set; } 
     public DateTime DateOfIssue { get; set; } 
     public List<string> Books { get; set; } 
    } 

和数据将显示如下：有没有按照我的期望什么错在我的视图模型：

特别注意（截图数据将通过上表的数据成功的分组后更换）？

以下一些stackoverflow答案后，我尝试了很多，但没有为我工作。任何帮助将不胜感激。

我曾尝试代码：

var viewmodel = from b in db.BookIssues 
       group b by new 
       { 
        b.IssuerName, 
        b.DateOfIssue 
       } 
       into g 
       select new ViewModel() 
       { 
        Name = g.key.IssuerName, 
        DateOfIssue = g.Key.DateOfIssue, 
        Books = g.ToList() //Actually this line of code is not working 
       }; 

Answer 1

书籍= g.ToList（）//其实这条线的工作不

大概是因为书籍属性的List<string>，不List<ActualClass>型。

能否请您尝试此查询，我添加b.Select(bn => bn.BookName).ToList()提取的书籍只有名称：x.IssuerName, x.DateOfIssue：

var books = new List<ActualClass> 
{ 
    new ActualClass { BookName = "A", DateOfIssue = new DateTime(2015, 10, 10, 10, 10, 0), IssuerName = "1" }, 
    new ActualClass { BookName = "B", DateOfIssue = new DateTime(2015, 10, 10, 10, 10, 0), IssuerName = "1" }, 
    new ActualClass { BookName = "C", DateOfIssue = new DateTime(2015, 10, 10, 10, 10, 0), IssuerName = "1" }, 
    new ActualClass { BookName = "D", DateOfIssue = new DateTime(2015, 10, 10, 10, 10, 0), IssuerName = "2" }, 
    new ActualClass { BookName = "E", DateOfIssue = new DateTime(2015, 10, 10, 12, 10, 0), IssuerName = "2" }, 
    new ActualClass { BookName = "F", DateOfIssue = new DateTime(2015, 10, 10, 12, 10, 0), IssuerName = "2" } 
}; 

var result = books.GroupBy(x => new { x.IssuerName, x.DateOfIssue }) 
       .Select(b => new ViewModel 
       { 
        Books = b.Select(bn => bn.BookName).ToList(), 
        // Accessing to DateOfIssue and IssuerName from Key. 
        DateOfIssue = b.Key.DateOfIssue, 
        IssuerName = b.Key.IssuerName 
       }); 

我的分组。我通过以下方式在GroupBy()中通过匿名输入：x => new { x.IssuerName, x.DateOfIssue }。

现在，他们都在关键的，你可以从KEY在以下访问发行者名称和DateOfIssue在SELECT语句，如：b.Key.IssuerName和b.Key.DateOfIssue。

Answer 2

如果您需要选择从组结果的书籍列表中，你需要Books = v.Select(c=>c.BookName).ToList()也注意到，在你的情况下，在发行日期时间时，你可能需要组仅由日期部分使用EntityFunctions.TruncateTime函数。如果你只存储日期，那么你可以忽略这个功能。

var viewmodel = db.BookIssues.GroupBy(x=>new {IssuerName =x.IssuerName, DateOfIssue=EntityFunctions.TruncateTime(x.DateOfIssue) }) 
.Select(v=>new ViewModel(){IssuerName =v.Key.IssuerName, DateOfIssue = v.Key.DateOfIssue, Books = v.Select(c=>c.BookName).ToList() }) 
.ToList();