Queryable.OrderByDescending Méthode

Définition

Trie les éléments d'une séquence dans l'ordre décroissant.Sorts the elements of a sequence in descending order.

Surcharges

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

Trie les éléments d'une séquence dans l'ordre décroissant selon une clé.Sorts the elements of a sequence in descending order according to a key.

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

Trie les éléments d'une séquence dans l'ordre décroissant à l'aide d'un comparateur spécifié.Sorts the elements of a sequence in descending order by using a specified comparer.

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

Trie les éléments d'une séquence dans l'ordre décroissant selon une clé.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)

Paramètres de type

TSource

Le type des éléments de source.The type of the elements of source.

TKey

Type de la clé retournée par la fonction représentée par keySelector.The type of the key returned by the function that is represented by keySelector.

Paramètres

source
IQueryable<TSource>

Séquence de valeurs à classer.A sequence of values to order.

keySelector
Expression<Func<TSource,TKey>>

Fonction permettant d'extraire une clé d'un élément.A function to extract a key from an element.

Retours

IOrderedQueryable<TSource>

IOrderedQueryable<T> dont les éléments sont triés dans l'ordre décroissant selon une clé.An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

Exceptions

source ou keySelector est null.source or keySelector is null.

Remarques

Cette méthode a au moins un paramètre de type Expression<TDelegate> dont l’argument de type est l’un des Func<T,TResult> types.This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. Pour ces paramètres, vous pouvez passer une expression lambda et elle sera compilée dans un Expression<TDelegate> .For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

La OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) méthode génère un MethodCallExpression qui représente l’appel de OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) lui-même comme une méthode générique construite.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. Il passe ensuite MethodCallExpression à la CreateQuery<TElement>(Expression) méthode de IQueryProvider représenté par la Provider propriété du source paramètre.It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. Le résultat de l’appel de CreateQuery<TElement>(Expression) est casté en type IOrderedQueryable<T> et retourné.The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

Le comportement de la requête qui se produit suite à l’exécution d’une arborescence d’expressions qui représente l’appel de OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) dépend de l’implémentation du type du source paramètre.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. Le comportement attendu est qu’il trie les éléments de source dans l’ordre décroissant, en fonction de la clé obtenue en appelant keySelector sur chaque élément de 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.

S’applique à

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

Trie les éléments d'une séquence dans l'ordre décroissant à l'aide d'un comparateur spécifié.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);
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)

Paramètres de type

TSource

Le type des éléments de source.The type of the elements of source.

TKey

Type de la clé retournée par la fonction représentée par keySelector.The type of the key returned by the function that is represented by keySelector.

Paramètres

source
IQueryable<TSource>

Séquence de valeurs à classer.A sequence of values to order.

keySelector
Expression<Func<TSource,TKey>>

Fonction permettant d'extraire une clé d'un élément.A function to extract a key from an element.

comparer
IComparer<TKey>

IComparer<T> pour comparer les clés.An IComparer<T> to compare keys.

Retours

IOrderedQueryable<TSource>

IOrderedQueryable<T> dont les éléments sont triés dans l'ordre décroissant selon une clé.An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

Exceptions

source ou keySelector ou comparer a la valeur null.source or keySelector or comparer is null.

Exemples

L’exemple de code suivant montre comment utiliser OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) pour trier les éléments d’une séquence dans l’ordre décroissant à l’aide d’un comparateur personnalisé.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

Remarques

Cette méthode a au moins un paramètre de type Expression<TDelegate> dont l’argument de type est l’un des Func<T,TResult> types.This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. Pour ces paramètres, vous pouvez passer une expression lambda et elle sera compilée dans un Expression<TDelegate> .For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

La OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) méthode génère un MethodCallExpression qui représente l’appel de OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) lui-même comme une méthode générique construite.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. Il passe ensuite MethodCallExpression à la CreateQuery<TElement>(Expression) méthode de IQueryProvider représenté par la Provider propriété du source paramètre.It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. Le résultat de l’appel de CreateQuery<TElement>(Expression) est casté en type IOrderedQueryable<T> et retourné.The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

Le comportement de la requête qui se produit suite à l’exécution d’une arborescence d’expressions qui représente l’appel de OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) dépend de l’implémentation du type du source paramètre.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. Le comportement attendu est qu’il trie les éléments de source dans l’ordre décroissant, en fonction de la clé obtenue en appelant keySelector sur chaque élément de 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. Le comparer paramètre est utilisé pour comparer des clés.The comparer parameter is used to compare keys.

S’applique à