Question

我必须修改一个查询以添加一个额外的连接来引入一个分区名称。

            var c = from C in db.Campaigns
                join L in db.Links on C.id equals L.campaignID into CL
                from CL2 in CL.DefaultIfEmpty()
                join D in db.Divisions on CL2.divisionID equals D.id into CLD
                from CLD2 in CLD.DefaultIfEmpty()
                where C.ClientID == user.ClientID
                group CLD2 by new { C.id, C.Name, Division = CLD2.Name, C.created } into G
                select new {
                    CampaignName = G.Key.Name,
                    Campaignid = G.Key.id,
                    Division = G.Key.Division ?? "-",
                    Created = G.Key.created,
                    Links = G.Count(b => b.Name != null) };

我遇到的问题是，当链接数为0时，每个行的分区名称为空（并且它不应该是）。

所以我尝试使用Lambda以不同的方式编写它：

var c = from CLD in ( from C in db.Campaigns from L in db.Links.Where(w => w.campaignID == C.id).DefaultIfEmpty() from D in db.Divisions.Where(w => w.id == C.DivisionID).DefaultIfEmpty() where C.ClientID == user.ClientID select new { CampaignName = C.Name, Campaignid = C.id, Division = D.Name, Created = C.created } ) group CLD by new { id = CLD.Campaignid, Name = CLD.CampaignName, Division = CLD.Division, created = CLD.Created } into G select new { CampaignName = G.Key.Name, Campaignid = G.Key.id, Division = G.Key.Division ?? "-", Created = G.Key.created, Links = G.Count(b => b.Campaignid != null) };

在此查询中，所有行的分区名称都正确显示，但当Links的数量为0时，查询返回1。

我确信我在两种情况下都很接近，但似乎无法找到正确的语法。欢迎任何建议。很高兴为任何一个查询修复，但最终会看到如何解决这两个问题。

谢谢大家。

Answer 1

好吧，我有人看着它并帮我整理一下。这是一个更简洁的查询，更完整的lambda比我的第二个更混乱。所以希望这个例子可以帮助其他人。

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Linq 2 SQL Join / Group with count

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