C# Linq到SQL计数生成超时的分组元素
我有一张这样的桌子：C# Linq到SQL计数生成超时的分组元素,c#,.net,linq,linq-to-sql,C#,.net,Linq,Linq To Sql,我有一张这样的桌子： FruitID | FruitType 23 | 2 215 | 2 256 | 1 643 | 3 我想通过FruitType获得计数，给定一个名为fruitid的fruitid列表。这就是我所拥有的： var TheCounter = (from f in MyDC.Fruits where TheFruitIDs.Contains(f.FruitID)
FruitID | FruitType
23 | 2
215 | 2
256 | 1
643 | 3
FruitTypefruitidfruitid列表。这就是我所拥有的：
var TheCounter = (from f in MyDC.Fruits
where TheFruitIDs.Contains(f.FruitID)
group f by 0 into TheFruits
select new MyCounterMode()
{
CountType1 = (int?) TheFruits.Where(f => f.FruitType == 1).Count() ?? 0,
CountType2 = (int?) TheFruits.Where(f => f.FruitType == 2).Count() ?? 0,
.... all the way to CountType6
}).Single();
这段代码可以工作，但问题是有时我会因为查询运行太长而出现超时错误。如何更改此代码以避免超时问题？您需要记住，每次迭代都会执行select
因此，请尝试以下方法：
'var TheCounter = (from f in MyDC.Fruits
group f by f.FruitID into TheFruits
select new KeyValuePair<int, int>(TheFruits.Key,TheFruits.Count())).ToDictionary(r=>r.Key,r=>r.Value);'
'var TheCounter=（来自MyDC.Fruits中的f
f组由f.FruitID变成盗窃品
选择新的KeyValuePair（TheFruits.Key，TheFruits.Count（））.ToDictionary（r=>r.Key，r=>r.Value）；'
这将为您提供一个字典，其中包含：Key-fructid，Value-Count您的LINQ为每个计数生成saperate sql，因此您需要使用盗窃结果来计算您的项目
试试这个
var TheCounter = (from f in MyDC.Fruits
where TheFruitIDs.Contains(f.FruitID)
group new {f.FruitType} by f.FruitType into TheFruits
select new MyCounterMode()
{
CountType1 = TheFruits.Count(f => f.FruitType == 1),
CountType2 = TheFruits.Count(f => f.FruitType == 2),
.... all the way to CountType6
}).Single();
您可以在内存中按var tempResult = (from f in MyDC.Fruits where TheFruitIDs.Contains(f.FruitID)).ToList();
var TheCounter = (from f in tempResult
group f by f.FruitType into TheFruits
select new MyCounterMode()
{
CountType1 = (int?) TheFruits.Count(f => f.FruitType == 1),
CountType2 = (int?) TheFruits.Count(f => f.FruitType == 2),
.... all the way to CountType6
}).Single();
进行查询的最简单方法是按
水果类型var countsDictionary = MyDC
.Fruits
.Where(f => TheFruitIDs.Contains(f.FruitID))
.GroupBy(
f => f.FruitType,
(fruitType, fruits) => new { FruitType = fruitType, Count = fruits.Count() }
)
.ToDictionary(c => c.FruitType, c => c.Count);
where部分中的水果ID列表，如果该列表非常大，则可能会减慢查询速度。除非从以前的数据库查询中创建此列表，否则对此您无能为力。在这种情况下，您应该尽量避免将水果ID列表拖到客户端。相反，您应该将选择ID的查询与统计类型的查询相结合。这将确保整个查询在服务器端执行
您似乎关心代码的结构更改。只要创建匿名对象，就很难编写可重用代码。你可以考虑只使用字典的计数或类似的东西。另一个选项是创建具有计数的动态对象。就个人而言，我不喜欢这个解决方案，但你可能会发现它很有用
为了简化代码，需要一个类来存储计数：
class TypeCount {
public TypeCount(Int32 type, Int32 count) {
Type = type;
Count = count;
}
public Int32 Type { get; private set; }
public Int32 Count { get; private set; }
}
基于元组序列，具有属性CountType0
、CountType1
、CountType2
等的动态对象：
class CountsDictionary : DynamicObject {
readonly IDictionary<Int32, Int32> counts;
public CountsDictionary(IEnumerable<TypeCount> typeCounts) {
if (typeCounts== null)
throw new ArgumentNullException("typeCounts");
this.counts = typeCounts.ToDictionary(c => c.Type, c => c.Count);
}
public override Boolean TryGetMember(GetMemberBinder binder, out Object result) {
Int32 value;
if (binder.Name.StartsWith("CountType") && Int32.TryParse(binder.Name.Substring(9), NumberStyles.None, CultureInfo.InvariantCulture, out value) && value >= 0) {
result = this.counts.ContainsKey(value) ? this.counts[value] : 0;
return true;
}
result = 0;
return false;
}
}
然后，您可以检索属性计数.CountType1
，计数.CountType2
和计数.CountType3
。其他count.CountType#
属性将返回0。但是，由于计数
是动态的，您将无法获得任何intellisense。这就是您的查询的含义：
SELECT
[Limit1].[C1] AS [C1],
[Limit1].[C2] AS [C2],
[Limit1].[C3] AS [C3],
[Limit1].[C4] AS [C4],
[Limit1].[C5] AS [C5],
[Limit1].[C6] AS [C6],
[Limit1].[C7] AS [C7]
FROM ( SELECT TOP (2)
[Project13].[C1] AS [C1],
CASE WHEN ([Project13].[C2] IS NULL) THEN 0 ELSE [Project13].[C3] END AS [C2],
CASE WHEN ([Project13].[C4] IS NULL) THEN 0 ELSE [Project13].[C5] END AS [C3],
CASE WHEN ([Project13].[C6] IS NULL) THEN 0 ELSE [Project13].[C7] END AS [C4],
CASE WHEN ([Project13].[C8] IS NULL) THEN 0 ELSE [Project13].[C9] END AS [C5],
CASE WHEN ([Project13].[C10] IS NULL) THEN 0 ELSE [Project13].[C11] END AS [C6],
CASE WHEN ([Project13].[C12] IS NULL) THEN 0 ELSE [Project13].[C13] END AS [C7]
FROM ( SELECT
[Project12].[C1] AS [C1],
[Project12].[C2] AS [C2],
[Project12].[C3] AS [C3],
[Project12].[C4] AS [C4],
[Project12].[C5] AS [C5],
[Project12].[C6] AS [C6],
[Project12].[C7] AS [C7],
[Project12].[C8] AS [C8],
[Project12].[C9] AS [C9],
[Project12].[C10] AS [C10],
[Project12].[C11] AS [C11],
[Project12].[C12] AS [C12],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent13]
WHERE ([Extent13].[FruitID] IN (23, 215, 256, 643)) AND ([Project12].[C1] = 0)
AND (6 = [Extent13].[FruitType])) AS [C13]
FROM ( SELECT
[Project11].[C1] AS [C1],
[Project11].[C2] AS [C2],
[Project11].[C3] AS [C3],
[Project11].[C4] AS [C4],
[Project11].[C5] AS [C5],
[Project11].[C6] AS [C6],
[Project11].[C7] AS [C7],
[Project11].[C8] AS [C8],
[Project11].[C9] AS [C9],
[Project11].[C10] AS [C10],
[Project11].[C11] AS [C11],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent12]
WHERE ([Extent12].[FruitID] IN (23, 215, 256, 643))
AND ([Project11].[C1] = 0)
AND (6 = [Extent12].[FruitType])) AS [C12]
FROM ( SELECT
[Project10].[C1] AS [C1],
[Project10].[C2] AS [C2],
[Project10].[C3] AS [C3],
[Project10].[C4] AS [C4],
[Project10].[C5] AS [C5],
[Project10].[C6] AS [C6],
[Project10].[C7] AS [C7],
[Project10].[C8] AS [C8],
[Project10].[C9] AS [C9],
[Project10].[C10] AS [C10],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent11]
WHERE ([Extent11].[FruitID] IN (23, 215, 256, 643))
AND([Project10].[C1] = 0)
AND (5 = [Extent11].[FruitType])) AS [C11]
FROM ( SELECT
[Project9].[C1] AS [C1],
[Project9].[C2] AS [C2],
[Project9].[C3] AS [C3],
[Project9].[C4] AS [C4],
[Project9].[C5] AS [C5],
[Project9].[C6] AS [C6],
[Project9].[C7] AS [C7],
[Project9].[C8] AS [C8],
[Project9].[C9] AS [C9],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent10]
WHERE ([Extent10].[FruitID] IN (23, 215, 256, 643))
AND ([Project9].[C1] = 0)
AND (5 = [Extent10].[FruitType])) AS [C10]
FROM ( SELECT
[Project8].[C1] AS [C1],
[Project8].[C2] AS [C2],
[Project8].[C3] AS [C3],
[Project8].[C4] AS [C4],
[Project8].[C5] AS [C5],
[Project8].[C6] AS [C6],
[Project8].[C7] AS [C7],
[Project8].[C8] AS [C8],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent9]
WHERE ([Extent9].[FruitID] IN (23, 215, 256, 643))
AND ([Project8].[C1] = 0)
AND (4 = [Extent9].[FruitType])) AS [C9]
FROM ( SELECT
[Project7].[C1] AS [C1],
[Project7].[C2] AS [C2],
[Project7].[C3] AS [C3],
[Project7].[C4] AS [C4],
[Project7].[C5] AS [C5],
[Project7].[C6] AS [C6],
[Project7].[C7] AS [C7],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent8]
WHERE ([Extent8].[FruitID] IN (23, 215, 256, 643))
AND ([Project7].[C1] = 0)
AND (4 = [Extent8].[FruitType])) AS [C8]
FROM ( SELECT
[Project6].[C1] AS [C1],
[Project6].[C2] AS [C2],
[Project6].[C3] AS [C3],
[Project6].[C4] AS [C4],
[Project6].[C5] AS [C5],
[Project6].[C6] AS [C6],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent7]
WHERE ([Extent7].[FruitID] IN (23, 215, 256, 643))
AND ([Project6].[C1] = 0)
AND (3 = [Extent7].[FruitType])) AS [C7]
FROM ( SELECT
[Project5].[C1] AS [C1],
[Project5].[C2] AS [C2],
[Project5].[C3] AS [C3],
[Project5].[C4] AS [C4],
[Project5].[C5] AS [C5],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent6]
WHERE ([Extent6].[FruitID] IN (23, 215, 256, 643))
AND ([Project5].[C1] = 0)
AND (3 = [Extent6].[FruitType])) AS [C6]
FROM ( SELECT
[Project4].[C1] AS [C1],
[Project4].[C2] AS [C2],
[Project4].[C3] AS [C3],
[Project4].[C4] AS [C4],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent5]
WHERE ([Extent5].[FruitID] IN (23, 215, 256, 643))
AND ([Project4].[C1] = 0)
AND (2 = [Extent5].[FruitType])) AS [C5]
FROM ( SELECT
[Project3].[C1] AS [C1],
[Project3].[C2] AS [C2],
[Project3].[C3] AS [C3],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent4]
WHERE ([Extent4].[FruitID] IN (23, 215, 256, 643))
AND ([Project3].[C1] = 0)
AND (2 = [Extent4].[FruitType])) AS [C4]
FROM ( SELECT
[Project2].[C1] AS [C1],
[Project2].[C2] AS [C2],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits] AS [Extent3]
WHERE ([Extent3].[FruitID] IN (23, 215, 256, 643))
AND ([Project2].[C1] = 0)
AND (1 = [Extent3].[FruitType])) AS [C3]
FROM ( SELECT
[Distinct1].[C1] AS [C1],
(SELECT
COUNT(1) AS [A1]
FROM [dbo].[Fruits]AS [Extent2]
WHERE ([Extent2].[FruitID] IN (23, 215, 256, 643))
AND ([Distinct1].[C1] = 0)
AND (1 = [Extent2].[FruitType])) AS [C2]
FROM ( SELECT DISTINCT
0 AS [C1]
FROM [dbo].[Fruits]AS [Extent1]
WHERE [Extent1].[FruitID] IN (23, 215, 256, 643)
) AS [Distinct1]
) AS [Project2]
) AS [Project3]
) AS [Project4]
) AS [Project5]
) AS [Project6]
) AS [Project7]
) AS [Project8]
) AS [Project9]
) AS [Project10]
) AS [Project11]
) AS [Project12]
) AS [Project13]
) AS [Limit1]
请注意，对于每个分组，将再次评估IN，从而为大量ID列表生成非常大的工作负载
你必须把工作分成两步
List<int> theFruitIDs = new List<int> { 23, 215, 256, 643 };
var theCounter = (from f in MyDC.Fruits
where theFruitIDs.Contains(f.FruitID)
group f by f.FruitType into theFruits
select new { fruitType = theFruits.Key, fruitCount = theFruits.Count() })
.ToList();
现在，您可以获取生成的列表并在内存中对其进行透视，以获得MyCounterMode
var thePivot = new MyCounterMode
{
CountType1 = theCounter.Where(x => x.fruitType == 1).Select(x => x.fruitCount).SingleOrDefault(),
CountType2 = theCounter.Where(x => x.fruitType == 2).Select(x => x.fruitCount).SingleOrDefault(),
CountType3 = theCounter.Where(x => x.fruitType == 3).Select(x => x.fruitCount).SingleOrDefault(),
};
下面是我如何实现这一点的（我构建了一个简单的控制台程序来演示）：
水果.cs
public class Fruit
{
public Fruit(int fruitId, int fruitType)
{
FruitId = fruitId;
FruitType = fruitType;
}
public int FruitId { get; set; }
public int FruitType { get; set; }
}
class Program
{
static void Main(string[] args)
{
// Data
var fruits = new List<Fruit>
{
new Fruit(23, 2),
new Fruit(215, 2),
new Fruit(256, 1),
new Fruit(643, 3)
};
// Query
var query = fruits
.GroupBy(x => x.FruitType)
.Select(x => new {Name = x.Key, Total = x.Count()});
// Output
foreach (var item in query)
{
Console.WriteLine(item.Name + ": " + item.Total);
}
Console.ReadLine();
}
}
Program.cs
public class Fruit
{
public Fruit(int fruitId, int fruitType)
{
FruitId = fruitId;
FruitType = fruitType;
}
public int FruitId { get; set; }
public int FruitType { get; set; }
}
class Program
{
static void Main(string[] args)
{
// Data
var fruits = new List<Fruit>
{
new Fruit(23, 2),
new Fruit(215, 2),
new Fruit(256, 1),
new Fruit(643, 3)
};
// Query
var query = fruits
.GroupBy(x => x.FruitType)
.Select(x => new {Name = x.Key, Total = x.Count()});
// Output
foreach (var item in query)
{
Console.WriteLine(item.Name + ": " + item.Total);
}
Console.ReadLine();
}
}
类程序
{
静态void Main（字符串[]参数）
{
//资料
var=新列表
{
新水果（23,2），
新水果（215,2），
新水果（256,1），
新水果（643,3）
};
//质疑
var query=fruits
.GroupBy（x=>x.groupType）
.Select（x=>new{Name=x.Key，Total=x.Count（）}）；
//输出
foreach（查询中的var项）
{
Console.WriteLine（item.Name+“：”+item.Total）；
}
Console.ReadLine（）；
}
}
您需要关注的是query
。使用GroupBy
后，您将有一个组列表。对于每个组，键
是分组的标准（这里是水果类型
）。然后，我们调用Count（）
来获取该组中元素的数量。在不受CountType限制的情况下，这里有一种动态方法：
int-typesOfCounts=6；
IEnumerable theCounter=水果列表，其中（x=>fruitids.Contains（x.frutid））；
Dictionary myCounterMode=新字典（）；
对于（变量i=1；ix.果树类型==i））；
}
返回myCounterMode；
您确定这会转换为单个查询吗？似乎该投影每行可能产生6个新查询。是这样吗？这并不能回答您的问题，但是Count（）
返回一个int
，而不是int？
，即使在转换为SQL时也是如此；因此，空合并操作符是不必要的（甚至可能不起作用）。这是因为当强制转换到int？
时，它将永远不会有空值，因为0的值不为空。我很惊讶这篇文章没有用一组额外的括号括起演员阵容，但这可能是复制粘贴的问题。您必须查看生成的SQL并在查询分析器中运行它。将f按0分组到盗窃结果中
这有什么意义？盗窃结果通常包含多少元素？虽然这在SQL中是正确的，这里，groupby 0
只进行1个组和一个查询。尽管如此，我也认为在内存中进行分组（数据透视）更好，因此数据库可以只专注于生成数据。不，我需要在数据库中填充分组和计数器对象，而不是在内存中填充。不，我需要在数据库中填充分组和计数器对象，而不是在内存中。我提出并解释的都是在数据库中完成的。名单上的“计数器”是
var thePivot = new MyCounterMode
{
CountType1 = theCounter.Where(x => x.fruitType == 1).Select(x => x.fruitCount).SingleOrDefault(),
CountType2 = theCounter.Where(x => x.fruitType == 2).Select(x => x.fruitCount).SingleOrDefault(),
CountType3 = theCounter.Where(x => x.fruitType == 3).Select(x => x.fruitCount).SingleOrDefault(),
};
public class Fruit
{
public Fruit(int fruitId, int fruitType)
{
FruitId = fruitId;
FruitType = fruitType;
}
public int FruitId { get; set; }
public int FruitType { get; set; }
}
class Program
{
static void Main(string[] args)
{
// Data
var fruits = new List<Fruit>
{
new Fruit(23, 2),
new Fruit(215, 2),
new Fruit(256, 1),
new Fruit(643, 3)
};
// Query
var query = fruits
.GroupBy(x => x.FruitType)
.Select(x => new {Name = x.Key, Total = x.Count()});
// Output
foreach (var item in query)
{
Console.WriteLine(item.Name + ": " + item.Total);
}
Console.ReadLine();
}
}
int typesOfCounts = 6;
IEnumerable<Fruit> theCounter = fruitList.Where(x => theFruitIDs.Contains(x.FruitID));
Dictionary<string, int> myCounterMode = new Dictionary<string, int>();
for (var i = 1; i < typesOfCounts + 1; i++)
{
string counterType = "CountTypeX";
counterType = counterType.Replace("X", i.ToString());
myCounterMode.Add(counterType, theCounter.Count(x => x.FruitType == i));
}
return myCounterMode;