Question

我无法理解Linq to Entities中的左外连接数。

我的查询是：

SELECT Locations.LocationId, Locations.LocationName, LocationPrizes.PrizeId, LocationPrizes.PrizeQuantity, Prizes.PrizeName, ISNULL(COUNT(WonPrizes.WonPrizeId), 0) AS WonPrizes 

FROM Locations 

INNER JOIN LocationPrizes ON Locations.LocationId = LocationPrizes.LocationId INNER JOIN Prizes ON LocationPrizes.PrizeId = Prizes.PrizeId 

LEFT OUTER JOIN WonPrizes ON Locations.LocationId = WonPrizes.LocationId AND Prizes.PrizeId = WonPrizes.PrizeId

GROUP BY Locations.LocationId, Locations.LocationName, LocationPrizes.PrizeId, LocationPrizes.PrizeQuantity, Prizes.PrizeName

我的Linq是：

var locationPrizes = from l in context.Locations
                       select new
                           {
                               l.LocationId,
                               l.LocationName,
                               Prizes = from o in l.LocationPrizes
                                        select new
                                            {
                                                o.PrizeId,
                                                o.PrizeQuantity,
                                                o.Prize.PrizeJson
                                            }
                           };

我无法确定左外连接部分是否正常工作。有什么指针吗？

Answer 1

如果您碰巧有来自LocationPrizes的关联 - ＆gt; WonPrizes你可以这样做：

var locationPrizes = 
    from l in context.Locations
    select new
    {
        l.LocationId,
        l.LocationName,
        Prizes = 
            from o in l.LocationPrizes 
            select new
            {
                o.PrizeId,
                o.PrizeQuantity,
                o.Prize.PrizeJson
                WonPrizes = o.WonPrizes.Count();
            }
    };

如果没有，这也会起作用（对我来说适用于下面的小编辑）：

var locationPrizes = 
    from l in context.Locations
    select new
    {
        l.LocationId,
        l.LocationName,
        Prizes = 
            from o in l.LocationPrizes 
            select new
            {
                o.PrizeId,
                o.PrizeQuantity,
                o.Prize.PrizeJson
                WonPrizes = 
                    (from w in context.WonPrizes
                     where w.PrizeId == o.PrizeId 
                        && w.LocationId == l.LocationId
                     select w)
                    .Count()
            }
    };

使用linq中的左外连接计数到实体

1 个答案: