Question

我很开心LINQ查询，并且在找出正确的方法来获取相关条目的计数时会停下来。

我有LINQ查询和

var result = (from OR in orders
                join OE in order_entries on OR.id equals OE.order_id into temp
                from LOE in temp.DefaultIfEmpty()
                group LOE  by new {OR.user_id, OR.site } into g
                select new {
                   col1 = g.Key.user_id,
                   col2 = g.Key.site,
                   count = g.Count() ,
                   cost = g.Sum( oe => oe.cost)
                }
);

这转向

SELECT 
    1 AS [C1], 
    [GroupBy1].[K1] AS [user_id], 
    [GroupBy1].[K2] AS [site], 
    [GroupBy1].[A1] AS [C2], 
    [GroupBy1].[A2] AS [C3]
    FROM ( SELECT 
        [Extent1].[user_id] AS [K1], 
        [Extent1].[site] AS [K2], 
        COUNT(1) AS [A1], 
        SUM([Extent2].[cost]) AS [A2]
        FROM  [dbo].[orders] AS [Extent1]
        LEFT OUTER JOIN [dbo].[order_entries] AS [Extent2] ON [Extent1].[id] = [Extent2].[order_id]
        GROUP BY [Extent1].[user_id], [Extent1].[site]
    )  AS [GroupBy1]

我在这里试图实现的是将Count（1）替换为Count（[Extent2]。[id]），这样如果没有与该命令关联的条目，我想显示0而不是1。

有人可以帮我更新LINQ查询来实现这一目标吗？

更新：

用下面的替换将返回我想要的结果，但这也会使我的sql查询执行得更慢..

g.Where(i => i.orders != null).Count(),

Answer 1

最简单的方法是使用subqueries：

    var qry = from o in orders
        select new {
            oid = o.ID,
            uid = o.UserId,
            site = o.Site,
            count = order_entries.Where(oe=>oe.OrderId == o.ID).Count(),
            cost = order_entries.Where(oe=>oe.OrderId == o.ID).Sum(oe=>oe.Cost)
            };

但是如果你想加入两个数据集，请使用：

    var qry = (from o in orders join oe in order_entries on o.ID equals oe.OrderId into grp 
        from g in grp.DefaultIfEmpty()
        select new{
            oid = o.ID,
            uid = o.UserId,
            site = o.Site,
            count = grp.Count(),
            cost = grp.Sum(e=>e.Cost)
            }).Distinct();

我坚信第二个查询可以使用 group 语句以最简单的方式编写。

这是一个完整的LinqPad示例：

void Main()
{

    List<TOrder> orders = new List<TOrder>{
        new TOrder(1, 1, "Site1"),
        new TOrder(2, 1, "Site1"),
        new TOrder(3, 2, "Site2"),
        new TOrder(4, 2, "Site2"),
        new TOrder(5, 3, "Site3")
        };

    List<TOrderEntry> order_entries = new List<TOrderEntry>{
        new TOrderEntry(1, 1, 5.5),
        new TOrderEntry(2, 1, 6.2),
        new TOrderEntry(3, 1, 4.9),
        new TOrderEntry(4, 1, 55.15),
        new TOrderEntry(5, 1, 0.97),
        new TOrderEntry(6, 2, 2.23),
        new TOrderEntry(7, 2, 95.44),
        new TOrderEntry(8, 2, 3.88),
        new TOrderEntry(9, 2, 7.77),
        new TOrderEntry(10, 3, 25.23),
        new TOrderEntry(11, 3, 31.13),
        new TOrderEntry(12, 4, 41.14)
        };

//      var qry = from o in orders
//          select new {
//              oid = o.ID,
//              uid = o.UserId,
//              site = o.Site,
//              count = order_entries.Where(oe=>oe.OrderId == o.ID).Count(),
//              cost = order_entries.Where(oe=>oe.OrderId == o.ID).Sum(oe=>oe.Cost)
//              };
//      qry.Dump();

        var qry = (from o in orders join oe in order_entries on o.ID equals oe.OrderId into grp 
            from g in grp.DefaultIfEmpty()
            //group g by g into ggg
            select new{
                oid = o.ID,
                uid = o.UserId,
                site = o.Site,
                count = grp.Count(),
                cost = grp.Sum(e=>e.Cost)
                }).Distinct();
        qry.Dump();
}


// Define other methods and classes here
class TOrder
{
    private int iid =0;
    private int uid =0;
    private string ssite=string.Empty;

    public TOrder(int _id, int _uid, string _site)
    {
        iid = _id;  
        uid = _uid;
        ssite = _site;
    }

    public int ID
    {
        get{return iid;}
        set{iid = value;}
    }

    public int UserId
    {
        get{return uid;}
        set{uid = value;}
    }

    public string Site
    {
        get{return ssite;}
        set{ssite = value;}
    }
}


class TOrderEntry
{
    private int iid = 0;
    private int oid = 0;
    private double dcost = .0;

    public TOrderEntry(int _iid, int _oid, double _cost)
    {
        iid = _iid;
        oid = _oid;
        dcost = _cost;
    }

    public int EntryId
    {
        get{return iid;}
        set{iid = value;}
    }

    public int OrderId
    {
        get{return oid;}
        set{oid = value;}
    }

    public double Cost
    {
        get{return dcost;}
        set{dcost = value;}
    }

}

LINQ Left with group by和count

1 个答案: