如何在linq列表中分组并在c＃linq中连接一些字符串

Question

我有一个名为“ HoldItems”的域实体，并且创建了HoldItems对象的列表。

该HoldItems的所有属性是：

public int TransactionNo;
public int TransactionID;
public int ItemNo;
public String ItemName;
public int Qty;
public double Price;
public double TotalPrice;
public double DiscountPrice;
public int ItemType;
public bool VatInclude;
public double VatPrice;
public string Note;
public List<HoldExtraMenu> ExtraMenuList;
public string BelongCategoryName;
public int BelongItemNo;
public int BelongItemIndex;
public int BelongCategoryID;

我写了一些这样的LINQ查询，其中selectedItemList表示List<DomainEntities.HoldItems>

var results = from myobject in selectedItemList
              where myobject.ItemType == 5
              where myobject.BelongItemIndex==selectedItemList.IndexOf(C)                                      
              orderby myobject.BelongCategoryName                                                                            
              select myobject;

现在的问题是，我需要将这个结果按BelongCategoryName分组，并使用添加“，”将ItemName的输出列连接起来

Answer 1

您可以达到以下要求：

var resultSet = 
       results.GroupBy(e => e.BelongCategoryName)
              .ToDictionary(e => e.Key, 
                  g => string.Join(",", g.Select(a => a.ItemName)));

resultSet现在是一个Dictionary<string, string> 。

或者，如果您要将上述查询链接到您已经开始的查询：

var results = (from myobject in selectedItemList
               where myobject.ItemType == 5
               where myobject.BelongItemIndex == selectedItemList.IndexOf(C)
               orderby myobject.BelongCategoryName
               group myobject by myobject.BelongCategoryName)
               .ToDictionary(e => e.Key,
                      g => string.Join(",", g.Select(a => a.ItemName)));

或仅使用查询语法：

var results = from myobject in selectedItemList
              where myobject.ItemType == 5
              where myobject.BelongItemIndex == selectedItemList.IndexOf(C)
              orderby myobject.BelongCategoryName
              group myobject by myobject.BelongCategoryName into h
              select new
              {
                   BelongCategoryName = h.Key,
                   ItemNames = string.Join(", ", from e in h select e.ItemName)
              };