编写复杂的Linq2SQL查询

Question

我有以下数据

范畴

• CategoryName
• CategoryID

产品

• ProductID
• ProductName
• CategoryID

项目

• ItemID
• ItemName
• ProductID

什么是查询，以便我得到多个列表，

ListOfCategory包含CategoryName和ListOfProduct<>

ListOfProduct包含ProductName和ListOfItems<>

ListOfItems<>包含ItemName和ItemID

 var cats = (from g in CMP.tblCategories
                        join proc in CMP.tblProducts
                        on g.CategoryID equals proc.CategoryID
                        join item in CMP.tblItems
                        on proc.ProductID equals item.ProductID
                        select new { Cat = g.Name, Pro = proc.Name, Itm = item.Name, ItmID = item.ItemID });

我知道这很不对，所以请帮帮我

Answer 1

您可以使用Linq中的子查询简化您的需求。

//获取包含所有详细信息的项目列表

var Items = (from g in CMP.tblCategories
                        join proc in CMP.tblProducts
                        on g.CategoryID equals proc.CategoryID
                        join item in CMP.tblItems
                        on proc.ProductID equals item.ProductID
                        select new { Category = g.Name, ProductName = proc.Name, ItemName = item.Name, ItemID = item.ItemID });

//Group by ProductName  to get a list of ProductName , List<Items>

 var Products  = (from i in Items
                   group i by i.CategoryName into g
                  select new { CategoryName = g.Key, 
                         Products = (from p in Items
                                    group p by p.ProductName into Productgroup
                                     select new {ProductName = Productgroup.Key,              Items = Productgroup})
}).ToList();