Linq 组外连接投影在视图模型上

Question

过去 2 天我一直在互联网上寻找解决方案，以找到对 BookId 上的以下 linq 查询进行分组的解决方案，但无济于事。查询有效，但我想重新组织它，以便它可以按 BookId 或 BookTitle 分组。

型号

Book(BookId, Title, Author, ISBN, Location,  BookTypeId, StockLogValue) 
Booktype(BookTypeId, BookTypeName)
Stock(StockId, bookId, quantity, date_added)
Transact (transactionId, TransactionTypeId, BookId, Quantity, TransactDate)
TransactionType( TransactionTypeId, TransactionTypeName)

控制器

public ActionResult Report(int? year, int? month, int? BkId)
    {
        var query = ReportYrMn( year, month, BkId);
        return View(query);
    }
     public IEnumerable ReportYrMn(int? year, int? month, int? BkId)
    {
        var query =
            (from bk in db.Books
             join tr in db.Transacts.Where(a => a.TransactDate.Month == month && a.TransactDate.Year == year && a.TransactType.TransactTypeName == "sale") on bk.BookId equals tr.BookId into trs
             from x in trs.DefaultIfEmpty()
             join tr2 in db.Transacts.Where(a => a.TransactDate.Month == month && a.TransactDate.Year == year && a.TransactType.TransactTypeName == "gift") on bk.BookId equals tr2.BookId into trs2
             from x2 in trs2.DefaultIfEmpty()
             select new ReportViewModel { BookTitle = bk.BookTitle ,BookId = bk.BookId, StockLogValue=bksty.StockLogValue, SaleTotal = trs.Sum(c => c.TransactQty), GiftTotal = trs2.Sum(c => c.TransactQty), SalesCount = trs.Count(), GiftCount = trs2.Count() });
        return query.AsEnumerable(); 
    }

感谢您的帮助

Answer 1

您的问题的直接解决方案是删除 from a in b.DefaultIfEmpty() 行。 A join - into is the same as GroupJoin，创建与左侧项目相关的集合，即属于一本书的集合 Transacs。这正是您想要的。

随后的 from 等同于 SelectMany，它再次将这些集合展平，为您留下一个平展的图书交易行列表。

所以这会做你想做的事：

var query =
    (from bk in db.Books
     join tr in db.Transacts
                  .Where(a => a.TransactDate.Month == month && a.TransactDate.Year == year && a.TransactType.TransactTypeName == "sale")
        on bk.BookId equals tr.BookId into trs
     join tr2 in db.Transacts
                   .Where(a => a.TransactDate.Month == month && a.TransactDate.Year == year && a.TransactType.TransactTypeName == "gift")
        on bk.BookId equals tr2.BookId into trs2
     select new ReportViewModel
            {
               BookTitle = bk.BookTitle,
               BookId = bk.BookId, 
               StockLogValue=bksty.StockLogValue, 
               SaleTotal = trs.Sum(c => c.TransactQty), 
               GiftTotal = trs2.Sum(c => c.TransactQty), 
               SalesCount = trs.Count(), 
               GiftCount = trs2.Count() 
            });

我询问了导航属性，因为它们几乎总是使查询更容易编写，因为您不需要笨拙的 joins。就您而言，差异并不大。如果 Book 有导航属性 Transacts 查询可能如下所示：

var query =
    (from bk in db.Books
     let sales = bk.Transacts
                   .Where(a => a.TransactDate.Month == month && a.TransactDate.Year == year && a.TransactType.TransactTypeName == "sale")
     let gifts = bk.Transacts
                   .Where(a => a.TransactDate.Month == month && a.TransactDate.Year == year && a.TransactType.TransactTypeName == "gift")
     select new ReportViewModel
           {
               BookTitle = bk.BookTitle,
               BookId = bk.BookId, 
               StockLogValue=bksty.StockLogValue, 
               SaleTotal = sales.Sum(c => c.TransactQty), 
               GiftTotal = gifts.Sum(c => c.TransactQty), 
               SalesCount = sales.Count(), 
               GiftCount = gifts.Count() 
           });

Linq 组外连接投影在视图模型上

Linq group outer joins projected on a viewmodel

c#

linq

asp.net-mvc-viewmodel

linq-group