Queryable.OrderByDescending Metoda

Definice

Seřadí prvky sekvence v sestupném pořadí.Sorts the elements of a sequence in descending order.

Přetížení

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

Seřadí prvky sekvence v sestupném pořadí podle klíče.Sorts the elements of a sequence in descending order according to a key.

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

Seřadí prvky sekvence v sestupném pořadí pomocí zadané porovnávací metody.Sorts the elements of a sequence in descending order by using a specified comparer.

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

Seřadí prvky sekvence v sestupném pořadí podle klíče.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)

Parametry typu

TSource

Typ prvků source .The type of the elements of source.

TKey

Typ klíče vrácený funkcí, který je reprezentován keySelector .The type of the key returned by the function that is represented by keySelector.

Parametry

source
IQueryable<TSource>

Sekvence hodnot, které mají být seřazeny.A sequence of values to order.

keySelector
Expression<Func<TSource,TKey>>

Funkce pro extrakci klíče z elementu.A function to extract a key from an element.

Návraty

IOrderedQueryable<TSource>

IOrderedQueryable<T>Jejichž prvky jsou seřazeny v sestupném pořadí podle klíče.An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

Výjimky

source nebo keySelector je null .source or keySelector is null.

Poznámky

Tato metoda má alespoň jeden parametr typu, Expression<TDelegate> jehož argumentem typu je jeden z Func<T,TResult> typů.This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. Pro tyto parametry můžete předat výraz lambda a bude zkompilován do Expression<TDelegate> .For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>)Metoda generuje MethodCallExpression , který reprezentuje volání OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) sebe sama jako vytvořenou obecnou metodu.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. Poté předá MethodCallExpression CreateQuery<TElement>(Expression) metodě IQueryProvider reprezentované Provider vlastností source parametru.It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. Výsledek volání CreateQuery<TElement>(Expression) je přetypování na typ IOrderedQueryable<T> a vráceno.The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

Chování dotazu, k němuž dojde v důsledku provádění stromu výrazu, který představuje volání, OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>) závisí na implementaci typu source parametru.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. Očekávané chování je, že Seřadí prvky source v sestupném pořadí na základě klíče získaného vyvoláním keySelector na každý prvek 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.

Platí pro

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

Seřadí prvky sekvence v sestupném pořadí pomocí zadané porovnávací metody.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)

Parametry typu

TSource

Typ prvků source .The type of the elements of source.

TKey

Typ klíče vrácený funkcí, který je reprezentován keySelector .The type of the key returned by the function that is represented by keySelector.

Parametry

source
IQueryable<TSource>

Sekvence hodnot, které mají být seřazeny.A sequence of values to order.

keySelector
Expression<Func<TSource,TKey>>

Funkce pro extrakci klíče z elementu.A function to extract a key from an element.

comparer
IComparer<TKey>

IComparer<T>K porovnání klíčů.An IComparer<T> to compare keys.

Návraty

IOrderedQueryable<TSource>

IOrderedQueryable<T>Jejichž prvky jsou seřazeny v sestupném pořadí podle klíče.An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

Výjimky

source nebo keySelector comparer je null .source or keySelector or comparer is null.

Příklady

Následující příklad kódu ukazuje, jak použít OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) k řazení prvků sekvence v sestupném pořadí pomocí vlastní porovnávací metody.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

Poznámky

Tato metoda má alespoň jeden parametr typu, Expression<TDelegate> jehož argumentem typu je jeden z Func<T,TResult> typů.This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. Pro tyto parametry můžete předat výraz lambda a bude zkompilován do Expression<TDelegate> .For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)Metoda generuje MethodCallExpression , který reprezentuje volání OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) sebe sama jako vytvořenou obecnou metodu.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. Poté předá MethodCallExpression CreateQuery<TElement>(Expression) metodě IQueryProvider reprezentované Provider vlastností source parametru.It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. Výsledek volání CreateQuery<TElement>(Expression) je přetypování na typ IOrderedQueryable<T> a vráceno.The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

Chování dotazu, k němuž dojde v důsledku provádění stromu výrazu, který představuje volání, OrderByDescending<TSource,TKey>(IQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) závisí na implementaci typu source parametru.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. Očekávané chování je, že Seřadí prvky source v sestupném pořadí na základě klíče získaného vyvoláním keySelector na každý prvek 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. comparerParametr se používá k porovnání klíčů.The comparer parameter is used to compare keys.

Platí pro