如何在LINQ中做GroupBy多列
SQL中类似的代码:
SELECT * FROM <TableName> GROUP BY <Column1>,<Column2>
如何将其转换为LINQ:
QuantityBreakdown
(
MaterialID int,
ProductID int,
Quantity float
)
INSERT INTO @QuantityBreakdown (MaterialID, ProductID, Quantity)
SELECT MaterialID, ProductID, SUM(Quantity)
FROM @Transactions
GROUP BY MaterialID, ProductID
当前回答
对于VB和匿名/lambda:
query.GroupBy(Function(x) New With {Key x.Field1, Key x.Field2, Key x.FieldN })
其他回答
从c# 7开始，你也可以使用值元组:
group x by (x.Column1, x.Column2)
or
.GroupBy(x => (x.Column1, x.Column2))
.GroupBy(x => x.Column1 + " " + x.Column2)
您还可以使用Tuple<>作为强类型分组。
from grouping in list.GroupBy(x => new Tuple<string,string,string>(x.Person.LastName,x.Person.FirstName,x.Person.MiddleName))
select new SummaryItem
{
LastName = grouping.Key.Item1,
FirstName = grouping.Key.Item2,
MiddleName = grouping.Key.Item3,
DayCount = grouping.Count(),
AmountBilled = grouping.Sum(x => x.Rate),
}
c# 7.1或更高版本，使用元组和推断元组元素名称(目前它只适用于对象的linq，当需要表达式树时不支持，例如someIQueryable.GroupBy(…)Github的问题):
// declarative query syntax
var result =
from x in inMemoryTable
group x by (x.Column1, x.Column2) into g
select (g.Key.Column1, g.Key.Column2, QuantitySum: g.Sum(x => x.Quantity));
// or method syntax
var result2 = inMemoryTable.GroupBy(x => (x.Column1, x.Column2))
.Select(g => (g.Key.Column1, g.Key.Column2, QuantitySum: g.Sum(x => x.Quantity)));
使用匿名类型的c# 3或更高版本:
// declarative query syntax
var result3 =
from x in table
group x by new { x.Column1, x.Column2 } into g
select new { g.Key.Column1, g.Key.Column2, QuantitySum = g.Sum(x => x.Quantity) };
// or method syntax
var result4 = table.GroupBy(x => new { x.Column1, x.Column2 })
.Select(g =>
new { g.Key.Column1, g.Key.Column2 , QuantitySum= g.Sum(x => x.Quantity) });
需要注意的一点是，您需要为Lambda表达式发送一个对象，而不能为类使用实例。
例子:
public class Key
{
public string Prop1 { get; set; }
public string Prop2 { get; set; }
}
这将进行编译，但每个循环将生成一个键。
var groupedCycles = cycles.GroupBy(x => new Key
{
Prop1 = x.Column1,
Prop2 = x.Column2
})
如果你不想命名键属性，然后检索它们，你可以这样做。这将正确地GroupBy并为您提供关键属性。
var groupedCycles = cycles.GroupBy(x => new
{
Prop1 = x.Column1,
Prop2= x.Column2
})
foreach (var groupedCycle in groupedCycles)
{
var key = new Key();
key.Prop1 = groupedCycle.Key.Prop1;
key.Prop2 = groupedCycle.Key.Prop2;
}
