Queryable.Where 方法

定義

根據述詞來篩選值序列。Filters a sequence of values based on a predicate.

多載

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

根據述詞來篩選值序列。Filters a sequence of values based on a predicate.

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

根據述詞來篩選值序列。Filters a sequence of values based on a predicate. 述詞函式的邏輯中使用各項目的索引。Each element's index is used in the logic of the predicate function.

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

根據述詞來篩選值序列。Filters a sequence of values based on a predicate.

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);
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)

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IQueryable<TSource>

要篩選的 IQueryable<T>An IQueryable<T> to filter.

predicate
Expression<Func<TSource,Boolean>>

用來測試每個項目是否符合條件的函式。A function to test each element for a condition.

傳回

IQueryable<TSource>

IQueryable<T>,其中包含輸入序列中符合 predicate 指定之條件的項目。An IQueryable<T> that contains elements from the input sequence that satisfy the condition specified by predicate.

例外狀況

sourcepredicatenullsource or predicate is null.

範例

下列程式碼範例示範如何使用 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 篩選序列。The following code example demonstrates how to use Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) to filter a sequence.

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

備註

這個方法至少有一個類型的參數 Expression<TDelegate> ,其型別引數是其中一種 Func<T,TResult> 類型。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 針對這些參數,您可以傳入 lambda 運算式,並將其編譯為 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>)方法 MethodCallExpression 會產生,代表呼叫 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 本身做為已建立的泛型方法。The Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) method generates a MethodCallExpression that represents calling Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) itself as a constructed generic method. 然後,它會將傳遞 MethodCallExpression 給以 CreateQuery(Expression) 參數的屬性所表示的方法 IQueryProvider Provider sourceIt then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

執行表示呼叫的運算式樹狀架構所產生的查詢行為, Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) 取決於參數類型的實作為 sourceThe query behavior that occurs as a result of executing an expression tree that represents calling Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) depends on the implementation of the type of the source parameter. 預期的行為是它會傳回 source 符合所指定之條件的元素 predicateThe expected behavior is that it returns the elements from source that satisfy the condition specified by predicate.

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

根據述詞來篩選值序列。Filters a sequence of values based on a predicate. 述詞函式的邏輯中使用各項目的索引。Each element's index is used in the logic of the predicate function.

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);
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)

類型參數

TSource

source 項目的類型。The type of the elements of source.

參數

source
IQueryable<TSource>

要篩選的 IQueryable<T>An IQueryable<T> to filter.

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

用來測試各項目是否符合條件的函式;此函式的第二個參數代表來源序列中項目的索引。A function to test each element for a condition; the second parameter of the function represents the index of the element in the source sequence.

傳回

IQueryable<TSource>

IQueryable<T>,其中包含輸入序列中符合 predicate 指定之條件的項目。An IQueryable<T> that contains elements from the input sequence that satisfy the condition specified by predicate.

例外狀況

sourcepredicatenullsource or predicate is null.

範例

下列程式碼範例示範如何使用 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 來根據包含每個專案之索引的述詞來篩選序列。The following code example demonstrates how to use Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) to filter a sequence based on a predicate that incorporates the index of each element.

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

備註

這個方法至少有一個類型的參數 Expression<TDelegate> ,其型別引數是其中一種 Func<T,TResult> 類型。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 針對這些參數,您可以傳入 lambda 運算式,並將其編譯為 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)方法 MethodCallExpression 會產生,代表呼叫 Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 本身做為已建立的泛型方法。The Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) method generates a MethodCallExpression that represents calling Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) itself as a constructed generic method. 然後,它會將傳遞 MethodCallExpression 給以 CreateQuery(Expression) 參數的屬性所表示的方法 IQueryProvider Provider sourceIt then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

執行表示呼叫的運算式樹狀架構所產生的查詢行為, Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) 取決於參數類型的實作為 sourceThe query behavior that occurs as a result of executing an expression tree that represents calling Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) depends on the implementation of the type of the source parameter. 預期的行為是它會傳回 source 符合所指定之條件的元素 predicateThe expected behavior is that it returns the elements from source that satisfy the condition specified by predicate. 每個來源元素的索引都會作為的第二個引數提供 predicateThe index of each source element is provided as the second argument to predicate.

適用於