C# 中 LINQ 中的按多列分组

我有一个类如下：

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

It has following data in the table:

我想将它们分组发行人名称 and 签发日期对于以下 viewModel 类：

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

And data will be displayed as follows: (Screenshot data will be replaced by the previous table data after successful grouping)

特别注意： 根据我的预期，我的 ViewModel 有什么问题吗？

在遵循一些 stackoverflow 答案后，我尝试了很多，但没有一个对我有用。任何帮助将不胜感激。

我尝试过的代码：

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
                };

Books = g.ToList() //其实这行是行不通的

大概是因为Books属性的类型是List<string>, not List<ActualClass>.

我添加了这个查询，您可以尝试一下吗b.Select(bn => bn.BookName).ToList()仅提取书籍名称：

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
                });

我按以下方式分组：x.IssuerName, x.DateOfIssue。我通过传递匿名类型来做到这一点GroupBy()通过以下方式：x => new { x.IssuerName, x.DateOfIssue }.

现在它们已成为关键，您可以访问发行人名称 and 签发日期from SELECT 语句中的 KEY 如下所示：b.Key.IssuerName and b.Key.DateOfIssue.