數量詞作業
更新:2007 年 11 月
數量詞作業會傳回 Boolean 值,指出序列中的部分或所有項目是否都符合條件。
下圖說明對兩個不同來源序列執行的兩個不同數量詞作業。第一個作業會問是否有一個或多個項目為字元 'A',而結果是 true。第二個作業會問是否所有項目都是字元 'A',而結果是 true。
下節會列出執行數量詞作業的標準查詢運算子方法。
方法
方法名稱 |
說明 |
C# 查詢運算式語法 |
Visual Basic 查詢運算式語法 |
詳細資訊 |
---|---|---|---|---|
All |
判斷序列中的項目是否全都符合條件。 |
不適用。 |
Aggregate … In … Into All(…) |
|
Any |
判斷序列中是否有任何項目會符合條件。 |
不適用。 |
Aggregate … In … Into Any() |
|
Contains |
判斷序列是否包含指定的項目。 |
不適用。 |
不適用。 |
查詢運算式語法範例
這些範例在 Visual Basic 中使用 Aggregate 子句,做為 LINQ 查詢中篩選條件的一部分。
下列範例使用 Aggregate 子句和 All<TSource> 擴充方法,以傳回集合中寵物年齡全都大於所指定年齡的人。
Class Person
Private _name As String
Private _pets As Pet()
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Property Pets() As Pet()
Get
Return _pets
End Get
Set(ByVal value As Pet())
_pets = value
End Set
End Property
End Class
Class Pet
Private _name As String
Private _age As Integer
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Property Age() As Integer
Get
Return _age
End Get
Set(ByVal value As Integer)
_age = value
End Set
End Property
End Class
Sub All()
Dim barley As New Pet With {.Name = "Barley", .Age = 4}
Dim boots As New Pet With {.Name = "Boots", .Age = 1}
Dim whiskers As New Pet With {.Name = "Whiskers", .Age = 6}
Dim bluemoon As New Pet With {.Name = "Blue Moon", .Age = 9}
Dim daisy As New Pet With {.Name = "Daisy", .Age = 3}
Dim charlotte As New Person With {.Name = "Charlotte", .Pets = New Pet() {barley, boots}}
Dim arlene As New Person With {.Name = "Arlene", .Pets = New Pet() {whiskers}}
Dim rui As New Person With {.Name = "Rui", .Pets = New Pet() {bluemoon, daisy}}
' Create the list of Person objects that will be queried.
Dim people As New System.Collections.Generic.List(Of Person)(New Person() {charlotte, arlene, rui})
Dim query = From pers In people _
Where (Aggregate pt In pers.Pets Into All(pt.Age > 2)) _
Select pers.Name
Dim sb As New System.Text.StringBuilder()
For Each name As String In query
sb.AppendLine(name)
Next
' Display the results.
MsgBox(sb.ToString())
' This code produces the following output:
' Arlene
' Rui
End Sub
下一個範例使用 Aggregate 子句和 Any 擴充方法,以傳回集合中至少有一隻寵物年齡大於所指定年齡的人。
Class Person
Private _name As String
Private _pets As Pet()
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Property Pets() As Pet()
Get
Return _pets
End Get
Set(ByVal value As Pet())
_pets = value
End Set
End Property
End Class
Class Pet
Private _name As String
Private _age As Integer
Public Property Name() As String
Get
Return _name
End Get
Set(ByVal value As String)
_name = value
End Set
End Property
Public Property Age() As Integer
Get
Return _age
End Get
Set(ByVal value As Integer)
_age = value
End Set
End Property
End Class
Sub Any()
Dim barley As New Pet With {.Name = "Barley", .Age = 4}
Dim boots As New Pet With {.Name = "Boots", .Age = 1}
Dim whiskers As New Pet With {.Name = "Whiskers", .Age = 6}
Dim bluemoon As New Pet With {.Name = "Blue Moon", .Age = 9}
Dim daisy As New Pet With {.Name = "Daisy", .Age = 3}
Dim charlotte As New Person With {.Name = "Charlotte", .Pets = New Pet() {barley, boots}}
Dim arlene As New Person With {.Name = "Arlene", .Pets = New Pet() {whiskers}}
Dim rui As New Person With {.Name = "Rui", .Pets = New Pet() {bluemoon, daisy}}
' Create the list of Person objects that will be queried.
Dim people As New System.Collections.Generic.List(Of Person)(New Person() {charlotte, arlene, rui})
Dim query = From pers In people _
Where (Aggregate pt In pers.Pets Into Any(pt.Age > 7)) _
Select pers.Name
Dim sb As New System.Text.StringBuilder()
For Each name As String In query
sb.AppendLine(name)
Next
' Display the results.
MsgBox(sb.ToString())
' This code produces the following output:
' Rui
End Sub
進一步了解如何執行量化作業
請參閱
工作
HOW TO:在執行階段動態指定述詞篩選條件 (C# 程式設計手冊)