Queryable.OrderByDescending Queryable.OrderByDescending Queryable.OrderByDescending Queryable.OrderByDescending Method

Definizione

Ordina in senso decrescente gli elementi di una sequenza.Sorts the elements of a sequence in descending order.

Overload

OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>)

Ordina gli elementi di una sequenza in modo decrescente in base a una chiave.Sorts the elements of a sequence in descending order according to a key.

OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)

Ordina in senso decrescente gli elementi di una sequenza usando un operatore di confronto specificato.Sorts the elements of a sequence in descending order by using a specified comparer.

OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>)

Ordina gli elementi di una sequenza in modo decrescente in base a una chiave.Sorts the elements of a sequence in descending order according to a key.

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IOrderedQueryable<TSource> ^ OrderByDescending(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, TKey> ^> ^ keySelector);
public static System.Linq.IOrderedQueryable<TSource> OrderByDescending<TSource,TKey> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector);
static member OrderByDescending : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Key>> -> System.Linq.IOrderedQueryable<'Source>
<Extension()>
Public Function OrderByDescending(Of TSource, TKey) (source As IQueryable(Of TSource), keySelector As Expression(Of Func(Of TSource, TKey))) As IOrderedQueryable(Of TSource)

Parametri di tipo

TSource

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

TKey

Il tipo della chiave restituita dalla funzione rappresentata dal keySelector.The type of the key returned by the function that is represented by keySelector.

Parametri

source
IQueryable<TSource>

Sequenza di valori da ordinare.A sequence of values to order.

keySelector
Expression<Func<TSource,TKey>>

Funzione per estrarre una chiave da un elemento.A function to extract a key from an element.

Restituisce

Un IOrderedQueryable<T> cui elementi vengono ordinati in senso decrescente in base a una chiave.An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

Eccezioni

source o keySelector è null.source or keySelector is null.

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 OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) metodo genera un MethodCallExpression che rappresenta una chiamata OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) stesso come un metodo generico costruito.The OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) method generates a MethodCallExpression that represents calling OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) itself as a constructed generic method. Passa quindi il MethodCallExpression per il CreateQuery<TElement>(Expression) metodo del IQueryProvider rappresentato dal Provider proprietà del source parametro.It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. Il risultato della chiamata al metodo CreateQuery<TElement>(Expression) viene eseguito il cast al tipo IOrderedQueryable<T> e restituiti.The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

Il comportamento delle query che si verifica in seguito all'esecuzione di un albero delle espressioni che rappresenta una chiamata OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) dipende dall'implementazione del tipo del source parametro.The query behavior that occurs as a result of executing an expression tree that represents calling OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) depends on the implementation of the type of the source parameter. Il comportamento previsto è che ordina gli elementi della source in ordine decrescente, in base alla chiave ottenuta chiamando keySelector su ogni elemento di source.The expected behavior is that it sorts the elements of source in descending order, based on the key obtained by invoking keySelector on each element of source.

OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)

Ordina in senso decrescente gli elementi di una sequenza usando un operatore di confronto specificato.Sorts the elements of a sequence in descending order by using a specified comparer.

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IOrderedQueryable<TSource> ^ OrderByDescending(System::Linq::IQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, TKey> ^> ^ keySelector, System::Collections::Generic::IComparer<TKey> ^ comparer);
public static System.Linq.IOrderedQueryable<TSource> OrderByDescending<TSource,TKey> (this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector, System.Collections.Generic.IComparer<TKey> comparer);
static member OrderByDescending : System.Linq.IQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Key>> * System.Collections.Generic.IComparer<'Key> -> System.Linq.IOrderedQueryable<'Source>
<Extension()>
Public Function OrderByDescending(Of TSource, TKey) (source As IQueryable(Of TSource), keySelector As Expression(Of Func(Of TSource, TKey)), comparer As IComparer(Of TKey)) As IOrderedQueryable(Of TSource)

Parametri di tipo

TSource

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

TKey

Il tipo della chiave restituita dalla funzione rappresentata dal keySelector.The type of the key returned by the function that is represented by keySelector.

Parametri

source
IQueryable<TSource>

Sequenza di valori da ordinare.A sequence of values to order.

keySelector
Expression<Func<TSource,TKey>>

Funzione per estrarre una chiave da un elemento.A function to extract a key from an element.

comparer
IComparer<TKey>

Oggetto IComparer<T> per confrontare le chiavi.An IComparer<T> to compare keys.

Restituisce

Un IOrderedQueryable<T> cui elementi vengono ordinati in senso decrescente in base a una chiave.An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

Eccezioni

Il parametro source, il parametro keySelector o il parametro comparer è null.source or keySelector or comparer is null.

Esempi

Esempio di codice seguente viene illustrato come utilizzare OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) per ordinare gli elementi di una sequenza in ordine decrescente usando un operatore di confronto personalizzato.The following code example demonstrates how to use OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) to sort the elements of a sequence in descending order by using a custom comparer.

/// <summary>
/// This IComparer class sorts by the fractional part of the decimal number.
/// </summary>
public class SpecialComparer : IComparer<decimal>
{
    /// <summary>
    /// Compare two decimal numbers by their fractional parts.
    /// </summary>
    /// <param name="d1">The first decimal to compare.</param>
    /// <param name="d2">The second decimal to compare.</param>
    /// <returns>1 if the first decimal's fractional part 
    /// is greater than the second decimal's fractional part,
    /// -1 if the first decimal's fractional
    /// part is less than the second decimal's fractional part,
    /// or the result of calling Decimal.Compare()
    /// if the fractional parts are equal.</returns>
    public int Compare(decimal d1, decimal d2)
    {
        decimal fractional1, fractional2;

        // Get the fractional part of the first number.
        try
        {
            fractional1 = decimal.Remainder(d1, decimal.Floor(d1));
        }
        catch (DivideByZeroException)
        {
            fractional1 = d1;
        }
        // Get the fractional part of the second number.
        try
        {
            fractional2 = decimal.Remainder(d2, decimal.Floor(d2));
        }
        catch (DivideByZeroException)
        {
            fractional2 = d2;
        }

        if (fractional1 == fractional2)
            return Decimal.Compare(d1, d2);
        else if (fractional1 > fractional2)
            return 1;
        else
            return -1;
    }
}

public static void OrderByDescendingEx1()
{
    List<decimal> decimals =
        new List<decimal> { 6.2m, 8.3m, 0.5m, 1.3m, 6.3m, 9.7m };

    // Sort the decimal values in descending order
    // by using a custom comparer.
    IEnumerable<decimal> query =
        decimals.AsQueryable()
        .OrderByDescending(num => num, new SpecialComparer());

    foreach (decimal num in query)
        Console.WriteLine(num);
}

/*
    This code produces the following output:

    9.7
    0.5
    8.3
    6.3
    1.3
    6.2
*/

''' <summary>
''' This class provides a custom implementation of the
''' IComparer.Compare() method. It sorts by the fractional part of the decimal number.
''' </summary>
Class SpecialComparer
    Implements IComparer(Of Decimal)

    ''' <summary>
    ''' Compare two decimal numbers by their fractional parts.
    ''' </summary>
    ''' <param name="d1">The first decimal to compare.</param>
    ''' <param name="d2">The second decimal to compare.</param>
    ''' <returns>1 if the first decimal's fractional part is greater than
    ''' the second decimal's fractional part,
    ''' -1 if the first decimal's fractional
    ''' part is less than the second decimal's fractional part,
    ''' or the result of calling Decimal.Compare()
    ''' if the fractional parts are equal.</returns>
    Function Compare(ByVal d1 As Decimal, ByVal d2 As Decimal) As Integer _
        Implements IComparer(Of Decimal).Compare

        Dim fractional1 As Decimal
        Dim fractional2 As Decimal

        ' Get the fractional part of the first number.
        Try
            fractional1 = Decimal.Remainder(d1, Decimal.Floor(d1))
        Catch ex As DivideByZeroException
            fractional1 = d1
        End Try

        ' Get the fractional part of the second number.
        Try
            fractional2 = Decimal.Remainder(d2, Decimal.Floor(d2))
        Catch ex As DivideByZeroException
            fractional2 = d2
        End Try

        If (fractional1 = fractional2) Then
            ' The fractional parts are equal, so compare the entire numbers.
            Return Decimal.Compare(d1, d2)
        ElseIf (fractional1 > fractional2) Then
            Return 1
        Else
            Return -1
        End If
    End Function
End Class

Sub OrderByDescendingEx1()
    ' Create a list of decimal values.
    Dim decimals As New List(Of Decimal)(New Decimal() _
                                         {6.2D, 8.3D, 0.5D, 1.3D, 6.3D, 9.7D})

    ' Order the elements of the list by passing
    ' in the custom IComparer class.
    Dim query As IEnumerable(Of Decimal) = _
        decimals.AsQueryable(). _
        OrderByDescending(Function(num) num, New SpecialComparer())

    Dim output As New System.Text.StringBuilder
    For Each num As Decimal In query
        output.AppendLine(num)
    Next

    ' Display the output.
    MsgBox(output.ToString())
End Sub

' This code produces the following output:

' 9.7
' 0.5
' 8.3
' 6.3
' 1.3
' 6.2

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 OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) metodo genera un MethodCallExpression che rappresenta una chiamata OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) stesso come un metodo generico costruito.The OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) method generates a MethodCallExpression that represents calling OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) itself as a constructed generic method. Passa quindi il MethodCallExpression per il CreateQuery<TElement>(Expression) metodo del IQueryProvider rappresentato dal Provider proprietà del source parametro.It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. Il risultato della chiamata al metodo CreateQuery<TElement>(Expression) viene eseguito il cast al tipo IOrderedQueryable<T> e restituiti.The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

Il comportamento delle query che si verifica in seguito all'esecuzione di un albero delle espressioni che rappresenta una chiamata OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) dipende dall'implementazione del tipo del source parametro.The query behavior that occurs as a result of executing an expression tree that represents calling OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) depends on the implementation of the type of the source parameter. Il comportamento previsto è che ordina gli elementi della source in ordine decrescente, in base alla chiave ottenuta chiamando keySelector su ogni elemento di source.The expected behavior is that it sorts the elements of source in descending order, based on the key obtained by invoking keySelector on each element of source. Il comparer parametro viene utilizzato per confrontare le chiavi.The comparer parameter is used to compare keys.

Si applica a