Queryable.Where Queryable.Where Queryable.Where Queryable.Where Method

Definizione

Filtra una sequenza di valori in base a un predicato.Filters a sequence of values based on a predicate.

Overload

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

Filtra una sequenza di valori in base a un predicato.Filters a sequence of values based on a predicate.

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

Filtra una sequenza di valori in base a un predicato.Filters a sequence of values based on a predicate. L'indice di ogni elemento viene usato nella logica della funzione predicato.Each element's index is used in the logic of the predicate function.

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

Filtra una sequenza di valori in base a un predicato.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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

Parametri

source
IQueryable<TSource>

Un IQueryable<T> da filtrare.An IQueryable<T> to filter.

predicate
Expression<Func<TSource,Boolean>>

Funzione per testare ogni elemento rispetto a una condizione.A function to test each element for a condition.

Restituisce

IQueryable<TSource>

Un' IQueryable<T> che contiene gli elementi dalla sequenza di input che soddisfano la condizione specificata dal predicate.An IQueryable<T> that contains elements from the input sequence that satisfy the condition specified by predicate.

Eccezioni

source o predicate è null.source or predicate is null.

Esempi

Esempio di codice seguente viene illustrato come utilizzare Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) per filtrare una sequenza.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

Commenti

Questo metodo ha almeno un parametro di tipo Expression<TDelegate> il cui argomento tipo è uno del Func<T,TResult> tipi.This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. Per questi parametri, è possibile passare in un'espressione lambda e verrà compilata per un Expression<TDelegate>.For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

Il Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) metodo genera un MethodCallExpression che rappresenta una chiamata Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) stesso come un metodo generico costruito.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. Passa quindi il MethodCallExpression per il CreateQuery(Expression) metodo del IQueryProvider rappresentato dal Provider proprietà del source parametro.It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

Il comportamento delle query che si verifica in seguito all'esecuzione di un albero delle espressioni che rappresenta una chiamata Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Boolean>>) dipende dall'implementazione del tipo del source parametro.The 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. Il comportamento previsto è che restituisce gli elementi dalla source che soddisfano la condizione specificata dal predicate.The 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>>) Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>)

Filtra una sequenza di valori in base a un predicato.Filters a sequence of values based on a predicate. L'indice di ogni elemento viene usato nella logica della funzione predicato.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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

Parametri

source
IQueryable<TSource>

Un IQueryable<T> da filtrare.An IQueryable<T> to filter.

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

Una funzione per testare ogni elemento una condizione. il secondo parametro della funzione rappresenta l'indice dell'elemento nella sequenza di origine.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.

Restituisce

IQueryable<TSource>

Un' IQueryable<T> che contiene gli elementi dalla sequenza di input che soddisfano la condizione specificata dal predicate.An IQueryable<T> that contains elements from the input sequence that satisfy the condition specified by predicate.

Eccezioni

source o predicate è null.source or predicate is null.

Esempi

Esempio di codice seguente viene illustrato come utilizzare Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) per filtrare una sequenza in base a un predicato che incorpora l'indice di ogni elemento.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

Commenti

Questo metodo ha almeno un parametro di tipo Expression<TDelegate> il cui argomento tipo è uno del Func<T,TResult> tipi.This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. Per questi parametri, è possibile passare in un'espressione lambda e verrà compilata per un Expression<TDelegate>.For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

Il Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) metodo genera un MethodCallExpression che rappresenta una chiamata Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) stesso come un metodo generico costruito.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. Passa quindi il MethodCallExpression per il CreateQuery(Expression) metodo del IQueryProvider rappresentato dal Provider proprietà del source parametro.It then passes the MethodCallExpression to the CreateQuery(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

Il comportamento delle query che si verifica in seguito all'esecuzione di un albero delle espressioni che rappresenta una chiamata Where<TSource>(IQueryable<TSource>, Expression<Func<TSource,Int32,Boolean>>) dipende dall'implementazione del tipo del source parametro.The 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. Il comportamento previsto è che restituisce gli elementi dalla source che soddisfano la condizione specificata dal predicate.The expected behavior is that it returns the elements from source that satisfy the condition specified by predicate. L'indice di ogni elemento di origine viene fornito come secondo argomento per predicate.The index of each source element is provided as the second argument to predicate.

Si applica a