将 T-SQL 转换为 Linq

Question

我正在使用 Entitry Framework 4.1，我正在努力理解如何将以下使用连接和聚合方法的查询转换为 DomainService 中的 Linq to Entities 调用。

SELECT     tblTime.Period As Timeline, COUNT(tblEngineeringDashboard_ItemList.ID) AS Items
FROM         tblEngineeringDashboard_ItemList INNER JOIN
                      tblTime ON tblEngineeringDashboard_ItemList.TimeID = tblTime.ID
GROUP BY tblTime.Period
ORDER BY tblTime.Period

谁能提供帮助。

可能的解决方案

Dim var = From i In ObjectContext.tblEngineeringDashboard_ItemList
                Join t In ObjectContext.tblTimes On i.TimeID Equals t.ID
                Group By i.TimeID Into Group
                Select DateStart = (From n In ObjectContext.tblTimes Where n.ID = TimeID Select n.Period), PartCount = Group.Count

菲尔

Answer 1

首先想到的是：

var q = from t in Context.Time
        group t by t.Period into g
        orderby g.Key
        select new 
        {
            Timeline = g.Key,
            Items = (from ti in g
                     from il in ti.ItemList // or whatever the property for the navigation to tblEngineeringDashboard_ItemList is called
                     select il).Count()
        };

但是，原始 SQL 有一个 INNER JOIN，它将拒绝 tblTime 记录，而 tblEngineeringDashboard_ItemList 中没有任何匹配记录。所以你可能想要：

var q = from t in Context.Time
        where t.ItemList.Any()
        group t by t.Period into g
        orderby g.Key
        select new 
        {
            Timeline = g.Key,
            Items = (from ti in g
                     from il in ti.ItemList // or whatever the property for the navigation to tblEngineeringDashboard_ItemList is called
                     select il).Count()
        };

您还可以翻转查询：

var q = from i in Context.EngineeringDashboardItemList
        where i.Time != null 
        group i by i.Time.Period into g
        orderby g.Key
        select new 
        {
            Timeline = g.Key,
            Items = g.Count()
        };

Answer 2

这行得通吗？

tblEngineeringDashboard_ItemList
    .Join(tblTime,ed => ed.TimeID ,t => t.ID, (ed,t) => new{ed,t})
.GoupBy(g => g.t.Period)
.Select(s => new 
          {
           Timeline = s.Key,
           Items = s.Count()
          }
       )
.OrderBy(o => o.Timeline)

Answer 3

虽然从 sql 转换为 linq 不是一种理想的方法（您应该直接在 linq 中思考，将您的需求转换为 linq 查询），但您发布的查询相当简单。

var grouped = tblTime.OrderBy(c => c.Period).GroupBy(c => c.Period).Select(c =>
new {
       timeline = c.Key,
       count = c.SelectMany(x => x.tblEngineeringDashboard).Count()
    });

*编辑：那里，已修复。 L2E 引擎上的一切。

前提是表之间有正确的外键（因此您不必手动声明连接）。