LINQ Group by 多列值在C#与VB.Net上写法的区别

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现有这样一个LIST，需要根据Age和Sex两列进行Group by 分组操作：

[csharp] view plaincopy

var empList =new List<Employee>
{
new Employee {ID = 1, FName = "John", Age = 23, Sex = 'M'},
new Employee {ID = 2, FName = "Mary", Age = 25, Sex = 'F'},
new Employee {ID = 3, FName = "Amber", Age = 23, Sex = 'M'},
new Employee {ID = 4, FName = "Kathy", Age = 25, Sex = 'F'},
new Employee {ID = 5, FName = "Lena", Age = 27, Sex = 'F'},
new Employee {ID = 6, FName = "Bill", Age = 28, Sex = 'M'},
new Employee {ID = 7, FName = "Celina", Age = 27, Sex = 'F'},
new Employee {ID = 8, FName = "John", Age = 28, Sex = 'M'}
};

用C# 很好实现，一般这样来写LINQ语句：

[csharp] view plaincopy

// query with lamda expression
var QueryWithLamda = empList.GroupBy(x => new { x.Age, x.Sex})
.Select(g=>new {g.Key, Count=g.Count()});
//query with standard expression
var query=from el in empList
group el by new {el.Age,el.Sex} into g
select new {g.Key, Count=g.Count()};

现在需要用VB.Net来实现，根据上边C#的写法，很容易想到这样来写：

[vb] view plaincopy

' query with lamda expression
Dim QueryWithLamda = empList.GroupBy(Function(x) New With { .Age=x.Age, .Sex= x.Sex}) _
.Select(Function(g) New With {g.Key, g.Count()})
' query with standard expression
Dim Query = From el In empList _
Group el By Key = new with { el.Age, el.Sex} Into g= Group _
Select New With {.key = Key, _
.count = g.Count()}

但是打印一下结果发现不对，后来仔细研究了下，原来问题出在这:

Group el By Key = new with {el.Age, el.Sex} Into g= Group _

换成这样，结果就和C#的一样了:

Group el By Key = new with{key el.Age, key el.Sex} Into g= Group _

看来在VB.NET中，匿名类和C#不一样，当Group by多列时，需要全部指定它们为Key，不然不会将它们作为一个整体进行group by

以下是全部代码:
C#:

void Main(){ var  empList =new List<Employee> {new Employee {ID = 1, FName = "John", Age = 23, Sex = 'M'},new Employee {ID = 2, FName = "Mary", Age = 25, Sex = 'F'},new Employee {ID = 3, FName = "Amber", Age = 23, Sex = 'M'},new Employee {ID = 4, FName = "Kathy", Age = 25, Sex = 'F'},new Employee {ID = 5, FName = "Lena", Age = 27, Sex = 'F'},new Employee {ID = 6, FName = "Bill", Age = 28, Sex = 'M'},new Employee {ID = 7, FName = "Celina", Age = 27, Sex = 'F'},new Employee {ID = 8, FName = "John", Age = 28, Sex = 'M'}  };// query with lamdaexpressionvar QueryWithLamda = empList.GroupBy(x => new { x.Age,  x.Sex})            .Select(g=>new {g.Key, Count=g.Count()}); //query with standard expressionvar query=from el in empList          group el by new {el.Age,el.Sex} into g  select new {g.Key, Count=g.Count()};  foreach (var employee in query /* Or  QueryWithLamda */ ) Console.WriteLine(employee.Count); }public class Employee{  public int ID {get;set;}  public string FName {get;set;}  public int Age {get;set;}  public char Sex {get;set;}}

VB.NET代码:

Sub Main Dim empList As New List(Of Employee)()empList.Add(New Employee() With _{.ID = 1, .FName = "John", .Age = 23, .Sex = "M"c}) empList.Add(New Employee() With _{.ID = 2, .FName = "Mary", .Age = 25, .Sex = "F"c})empList.Add(New Employee() With _{.ID = 3, .FName = "Amber", .Age = 23, .Sex = "M"c}) empList.Add(New Employee() With _{.ID = 4, .FName = "Kathy", .Age = 25, .Sex = "F"c})empList.Add(New Employee() With _{.ID = 5, .FName = "Lena", .Age = 27, .Sex = "F"c}) empList.Add(New Employee() With _{.ID = 6, .FName = "Bill", .Age = 28, .Sex = "M"c})empList.Add(New Employee() With _{.ID = 7, .FName = "Celina", .Age = 27, .Sex = "F"c}) empList.Add(New Employee() With _{.ID = 8, .FName = "John", .Age = 28, .Sex = "M"c})' query with lamdaexpressionDim QueryWithLamda = empList.GroupBy(Function(x)  New With { Key x.Age, Key x.Sex}) _            .Select(Function(g) New With {g.Key, g.Count()}) ' query with standard expressionDim QueryWithStanard = From el In empList _     Group el By Key = new with {Key el.Age, Key el.Sex} Into g= Group  _     Select New  With {.key = Key, _.count = g.Count()} Dim QueryWithStanard2 = From el In empList _     Group el By Key = el.Age,  el.Sex  Into g= Group  _     Select New  With {.key = Key, _.count = g.Count()}  For Each employee In QueryWithLamda  'Or  QueryWithLamda Console.WriteLine(employee.Count)Next employee End SubPublic Class Employee Private privateID As IntegerPublic Property ID() As Integer Get Return privateIDEnd Get Set(ByVal value As Integer) privateID = valueEnd Set End Property Private privateFName As String Public Property FName() As StringGet Return privateFNameEnd Get Set(ByVal value As String) privateFName = valueEnd Set End Property  Private privateAge As Integer Public Property Age() As IntegerGet Return privateAgeEnd Get Set(ByVal value As Integer) privateAge = valueEnd Set End Property  Private privateSex As Char Public Property Sex() As CharGet Return privateSexEnd Get Set(ByVal value As Char) privateSex = valueEnd Set End PropertyEnd Class

[vb] view plaincopy

Sub Main
Dim empList As New List(Of Employee)()
empList.Add(New Employee() With _
{.ID = 1, .FName = "John", .Age = 23, .Sex = "M"c})
empList.Add(New Employee() With _
{.ID = 2, .FName = "Mary", .Age = 25, .Sex = "F"c})
empList.Add(New Employee() With _
{.ID = 3, .FName = "Amber", .Age = 23, .Sex = "M"c})
empList.Add(New Employee() With _
{.ID = 4, .FName = "Kathy", .Age = 25, .Sex = "F"c})
empList.Add(New Employee() With _
{.ID = 5, .FName = "Lena", .Age = 27, .Sex = "F"c})
empList.Add(New Employee() With _
{.ID = 6, .FName = "Bill", .Age = 28, .Sex = "M"c})
empList.Add(New Employee() With _
{.ID = 7, .FName = "Celina", .Age = 27, .Sex = "F"c})
empList.Add(New Employee() With _
{.ID = 8, .FName = "John", .Age = 28, .Sex = "M"c})
' query with lamda expression
Dim QueryWithLamda = empList.GroupBy(Function(x) New With { Key x.Age, Key x.Sex}) _
.Select(Function(g) New With {g.Key, g.Count()})
' query with standard expression
Dim QueryWithStanard = From el In empList _
Group el By Key = new with {Key el.Age, Key el.Sex} Into g= Group _
Select New With {.key = Key, _
.count = g.Count()}
Dim QueryWithStanard2 = From el In empList _
Group el By Key = el.Age, el.Sex Into g= Group _
Select New With {.key = Key, _
.count = g.Count()}
For Each employee In QueryWithLamda 'Or QueryWithLamda
Console.WriteLine(employee.Count)
Next employee
End Sub
Public Class Employee
Private privateID As Integer
Public Property ID() As Integer
Get
Return privateID
End Get
Set(ByVal value As Integer)
privateID = value
End Set
End Property
Private privateFName As String
Public Property FName() As String
Get
Return privateFName
End Get
Set(ByVal value As String)
privateFName = value
End Set
End Property
Private privateAge As Integer
Public Property Age() As Integer
Get
Return privateAge
End Get
Set(ByVal value As Integer)
privateAge = value
End Set
End Property
Private privateSex As Char
Public Property Sex() As Char
Get
Return privateSex
End Get
Set(ByVal value As Char)
privateSex = value
End Set
End Property
End Class