限定符操作
限定符运算返回一个 Boolean 值,该值指示序列中是否有一些元素满足条件或是否所有元素都满足条件。
下图描述了两个不同源序列上的两个不同限定符运算。 第一个运算询问是否有一个或多个元素为字符“A”,结果为 true。 第二个运算询问是否所有元素都为字符“A”,结果为 true。
以下部分列出了执行限定符运算的标准查询运算符方法。
方法
方法名 |
说明 |
C# 查询表达式语法 |
Visual Basic 查询表达式语法 |
更多信息 |
---|---|---|---|---|
全部 |
确定是否序列中的所有元素都满足条件。 |
不适用。 |
Aggregate … In … Into All(…) |
|
Any |
确定序列中是否有元素满足条件。 |
不适用。 |
Aggregate … In … Into Any() |
|
Contains |
确定序列是否包含指定的元素。 |
不适用。 |
不适用。 |
查询表达式语法示例
下面这些示例将 Visual Basic 中的 Aggregate 子句用作 LINQ 查询中的筛选条件的一部分。
第一个示例使用 Aggregate 子句和 All<TSource> 扩展方法从集合中返回其宠物的年龄全都大于指定年龄的人员。
Class Person
Public Property Name As String
Public Property Pets As Pet()
End Class
Class Pet
Public Property Name As String
Public Property Age As Integer
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
第二个示例使用 Aggregate 子句和 Any 扩展方法从集合中返回那些至少有一只宠物的年龄大于指定年龄的人员。
Class Person
Public Property Name As String
Public Property Pets As Pet()
End Class
Class Pet
Public Property Name As String
Public Property Age As Integer
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