Queryable.Where 方法

定义

命名空间:: System.Linq

程序集:: System.Core.dll, System.Linq.Queryable.dll

程序集:: netstandard.dll, System.Linq.Queryable.dll

程序集:: System.Linq.Queryable.dll

程序集:: System.Core.dll

程序集:: netstandard.dll

重要

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根据谓词筛选值序列。

重载

名称	说明
Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)	根据谓词筛选值序列。
Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)	根据谓词筛选值序列。每个元素的索引都在谓词函数的逻辑中使用。

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

根据谓词筛选值序列。

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TSource> ^ Where(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, bool> ^> ^ predicate);

public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);

[System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")]
public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,bool>> predicate);

static member Where : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> System.Linq.IQueryable<'Source>

[<System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")>]
static member Where : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, bool>> -> System.Linq.IQueryable<'Source>

<Extension()>
Public Function Where(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Boolean))) As IQueryable(Of TSource)

类型参数

TSource

的元素 source的类型。

参数

source: IQueryable<TSource>

要筛选的一个 IQueryable<T> 。

predicate: Expression<Func<TSource,Boolean>>

用于测试条件的每个元素的函数。

IQueryable<TSource>

一个包含输入序列中满足由predicate指定条件的元素的元素IQueryable<T>。

属性: RequiresDynamicCodeAttribute

例外

ArgumentNullException

source 或 predicate 为 null.

示例

下面的代码示例演示如何用于 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 筛选序列。

List<string> fruits =
    new List<string> { "apple", "passionfruit", "banana", "mango",
                       "orange", "blueberry", "grape", "strawberry" };

// Get all strings whose length is less than 6.
IEnumerable<string> query =
    fruits.AsQueryable().Where(fruit => fruit.Length < 6);

foreach (string fruit in query)
    Console.WriteLine(fruit);

/*
    This code produces the following output:

    apple
    mango
    grape
*/

Dim fruits As New List(Of String)(New String() _
                        {"apple", "passionfruit", "banana", "mango", _
                         "orange", "blueberry", "grape", "strawberry"})

' Get all strings whose length is less than 6.
Dim query = fruits.AsQueryable().Where(Function(fruit) fruit.Length < 6)

' Display the results.
Dim output As New System.Text.StringBuilder
For Each fruit As String In query
    output.AppendLine(fruit)
Next
MsgBox(output.ToString())

' This code produces the following output:

' apple
' mango
' grape

注解

此方法至少有一个类型 Expression<TDelegate> 参数，其类型参数为类型之 Func<T,TResult> 一。对于这些参数，可以传入 lambda 表达式，并将它编译为一个 Expression<TDelegate>。

该方法Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)生成一个表示调用Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)自身为已构造泛型方法的一MethodCallExpression个方法。然后，它将传递给MethodCallExpression CreateQuery(Expression)由参数属性source表示Provider的方法IQueryProvider。

执行表示调用 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 的表达式树导致的查询行为取决于参数类型的 source 实现。预期行为是，它返回满足指定predicate条件的元素source。

适用于

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

Source:: Queryable.cs

根据谓词筛选值序列。每个元素的索引都在谓词函数的逻辑中使用。

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IQueryable<TSource> ^ Where(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, int, bool> ^> ^ predicate);

public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,bool>> predicate);

[System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")]
public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,int,bool>> predicate);

static member Where : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, bool>> -> System.Linq.IQueryable<'Source>

[<System.Diagnostics.CodeAnalysis.RequiresDynamicCode("Enumerating collections as IQueryable can require creating new generic types or methods, which requires creating code at runtime. This may not work when AOT compiling.")>]
static member Where : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, int, bool>> -> System.Linq.IQueryable<'Source>

<Extension()>
Public Function Where(Of TSource) (source As IQueryable(Of TSource), predicate As Expression(Of Func(Of TSource, Integer, Boolean))) As IQueryable(Of TSource)

类型参数

TSource

的元素 source的类型。

参数

source: IQueryable<TSource>

要筛选的一个 IQueryable<T> 。

predicate: Expression<Func<TSource,Int32,Boolean>>

用于测试条件的每个元素的函数;函数的第二个参数表示源序列中元素的索引。

IQueryable<TSource>

一个包含输入序列中满足由predicate指定条件的元素的元素IQueryable<T>。

属性: RequiresDynamicCodeAttribute

例外

ArgumentNullException

source 或 predicate 为 null.

示例

下面的代码示例演示如何 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 根据包含每个元素索引的谓词筛选序列。

int[] numbers = { 0, 30, 20, 15, 90, 85, 40, 75 };

// Get all the numbers that are less than or equal to
// the product of their index in the array and 10.
IEnumerable<int> query =
    numbers.AsQueryable()
    .Where((number, index) => number <= index * 10);

foreach (int number in query)
    Console.WriteLine(number);

/*
    This code produces the following output:

    0
    20
    15
    40
*/

Dim numbers() As Integer = {0, 30, 20, 15, 90, 85, 40, 75}

' Get all the numbers that are less than or equal to
' the product of their index in the array and 10.
Dim query = numbers.AsQueryable() _
    .Where(Function(number, index) number <= index * 10)

' Display the results.
Dim output As New System.Text.StringBuilder
For Each number As Integer In query
    output.AppendLine(number)
Next
MsgBox(output.ToString())

' This code produces the following output:

' 0
' 20
' 15
' 40

注解

该方法Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)生成一个表示调用Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)自身为已构造泛型方法的一MethodCallExpression个方法。然后，它将传递给MethodCallExpression CreateQuery(Expression)由参数属性source表示Provider的方法IQueryProvider。

执行表示调用 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 的表达式树导致的查询行为取决于参数类型的 source 实现。预期行为是，它返回满足指定predicate条件的元素source。每个源元素的索引作为第二个参数 predicate提供。

适用于

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通过

Queryable.Where 方法

定义

重载

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)

类型参数

参数

返回

例外

示例

注解

适用于

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)

类型参数

参数

返回

例外

示例

注解

适用于

反馈