[英]Refactoring the following LINQ query to perform better and look more simple
考虑一个函数(GetData),该函数返回以下结果集,其中第一列是部门ID,第二列是“ TotalSales”:
DivisionID: 3 500
DivisionID: 3 500
DivisionID: 3 500
DivisionID: 4 800
DivisionID: 4 800
DivisionID: 5 50
我需要编写一个LINQ查询来获得以下结果:
DiviosnID 3: (500 * 3) - 500 = 1000
DiviosnID 4: (800 * 2) - 800 = 800
DiviosnID 5: 0 /*this since it's happening only once*/
因此总数变为:1000 + 800 = 1800
最后,该值应乘以-1,得出-1800。
下面的LINQ查询可以完成工作,但是,IMSHO令人恐惧。 问题是,是否可以重写它以更快地执行并看起来更好? 请注意,这里有第三列,就像名为“ TotalPurchases”的TotalSales一样,我需要对其进行相同的计算。
GetData()
.Where(t => t.DivisionId != 0)
.GroupBy(t => t.DivisionId)
.Where(g => g.Count() > 1)
.Select(g => new MyEntity
{
TotalSales = g.Sum(n => n.TotalSales) - (g.Sum(n => n.TotalSales) / g.Count()),
TotalPurchases = g.Sum(n => n.TotalPurchases) - (g.Sum(n => n.TotalPurchases) / g.Count())
})
.Union(Enumerable.Repeat(new MyEntity(), 1))
.Aggregate((t1, t2) => new MyEntity
{
TotalSales = -(t1.TotalSales + t2.TotalSales),
TotalPurchases = -(t1.TotalPurchases + t2.TotalPurchases),
});
谢谢
快速的第一次尝试:
var consolidatedData = GetData()
.GroupBy(t => t.DivisionId)
.Where(g => g.Skip(1).Any(i => i.DivisionId != 0))
.Select(g => new
{
TotalSales = -(g.Sum(n => n.TotalSales) - g.Average(n => n.TotalSales)),
TotalPurchases = -(g.Sum(n => n.TotalPurchases) - g.Average(n => n.TotalPurchases))
});
var overallSales = consolidatedData.Sum(i => i.TotalSales);
var overallPurchases = consolidatedData.Sum(i => i.TotalPurchases);
使用“跳过”,可以避免在每个组上运行潜在昂贵的Count()-它仅跳过一项,然后查看是否还有剩余。
通过将结果构建到一个匿名对象的IEnumerable中,可以简化代码-然后,您可以在需要最终总和时查询它。 请注意,平均值也用于代替总和/计数。
聚合被删除-仅在需要时才计算最终总和。
我的主张:
var result = data
.Where(t => t.DivisionID != 0)
.GroupBy(t => t.DivisionID)
.Select(g => new MyEntity
{
TotalSales = g.Sum(n => n.TotalSales) - g.Average(n => n.TotalSales),
TotalPurchases = g.Sum(n => n.TotalPurchases) - g.Average(n => n.TotalPurchases)
})
.Aggregate(new MyEntity(), (t1, t2) => new MyEntity
{
TotalSales = t1.TotalSales - t2.TotalSales,
TotalPurchases = t1.TotalPurchases - t2.TotalPurchases,
});
Where(g => g.Count() > 1)
检查Where(g => g.Count() > 1)
,因为1个元素组的SUM和AVG相等,因此select将返回0。我还删除了Union(Enumerable.Repeat(new MyEntity(), 1))
然后将seed
添加到聚合调用中-这是初始值。
另一个:
var result = data
.Where(t => t.DivisionID != 0)
.GroupBy(t => t.DivisionID)
.Select(g => new MyEntity
{
TotalSales = g.Sum(n => n.TotalSales) - g.Average(n => n.TotalSales),
TotalPurchases = g.Sum(n => n.TotalPurchases) - g.Average(n => n.TotalPurchases)
})
.GroupBy(t => 0) // create single group
.Select(g => new MyEntity
{
TotalSales = -g.Sum(t => t.TotalSales),
TotalPurchases = -g.Sum(t => t.TotalPurchases)
})
.SingleOrDefault();
假设TotalSales
对于DivisionId
是常量,则可以使用:
var result = data
.Where(t => t.DivisionID != 0)
.GroupBy(t => t.DivisionID)
.Select(g => new MyEntity
{
TotalSales = g.Skip(1).Sum(n => n.TotalSales),
TotalPurchases = g.Skip(1).Sum(n => n.TotalPurchases)
})
.Aggregate(new MyEntity(), (t1, t2) => new MyEntity
{
TotalSales = t1.TotalSales - t2.TotalSales,
TotalPurchases = t1.TotalPurchases - t2.TotalPurchases,
});
var result = data
.Where(t => t.DivisionID != 0)
.GroupBy(t => t.DivisionID)
.Select(g => new MyEntity
{
TotalSales = g.Skip(1).Sum(n => n.TotalSales),
TotalPurchases = g.Skip(1).Sum(n => n.TotalPurchases)
})
.GroupBy(t => 0) // create single group
.Select(g => new MyEntity
{
TotalSales = -g.Sum(t => t.TotalSales),
TotalPurchases = -g.Sum(t => t.TotalPurchases)
})
.SingleOrDefault();
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