Queryable.ThenByDescending 方法

定义

按降序对序列中的元素执行后续排序。Performs a subsequent ordering of the elements in a sequence in descending order.

重载

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>)

根据某个键按降序对序列中的元素执行后续排序。Performs a subsequent ordering of the elements in a sequence in descending order, according to a key.

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)

使用指定的比较器按降序对序列中的元素执行后续排序。Performs a subsequent ordering of the elements in a sequence in descending order by using a specified comparer.

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>)

根据某个键按降序对序列中的元素执行后续排序。Performs a subsequent ordering of the elements in a sequence in descending order, according to a key.

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

类型参数

TSource

source 的元素类型。The type of the elements of source.

TKey

keySelector 表示的函数返回的键类型。The type of the key returned by the function represented by keySelector.

参数

source
IOrderedQueryable<TSource>

一个包含要排序的元素的 IOrderedQueryable<T>An IOrderedQueryable<T> that contains elements to sort.

keySelector
Expression<Func<TSource,TKey>>

用于从每个元素中提取键的函数。A function to extract a key from each element.

返回

一个 IOrderedQueryable<T>,将根据键按降序对其元素进行排序。An IOrderedQueryable<T> whose elements are sorted in descending order according to a key.

例外

sourcekeySelectornullsource or keySelector is null.

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) 本身。The ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) method generates a MethodCallExpression that represents calling ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderCreateQuery<TElement>(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. 调用 CreateQuery<TElement>(Expression) 的结果将强制转换为类型 IOrderedQueryable<T> 并返回。The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

因执行表示调用 ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>) depends on the implementation of the type of the source parameter. 预期的行为是根据通过对每个 source元素调用 keySelector 获取的键,按降序对 source 的元素执行次要排序。The expected behavior is that it performs a secondary sort of the elements of source in descending order, based on the key obtained by invoking keySelector on each element of source. 所有以前建立的排序顺序都将保留。All previously established sort orders are preserved.

ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>)

使用指定的比较器按降序对序列中的元素执行后续排序。Performs a subsequent ordering of the elements in 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> ^ ThenByDescending(System::Linq::IOrderedQueryable<TSource> ^ source, System::Linq::Expressions::Expression<Func<TSource, TKey> ^> ^ keySelector, System::Collections::Generic::IComparer<TKey> ^ comparer);
public static System.Linq.IOrderedQueryable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedQueryable<TSource> source, System.Linq.Expressions.Expression<Func<TSource,TKey>> keySelector, System.Collections.Generic.IComparer<TKey> comparer);
static member ThenByDescending : System.Linq.IOrderedQueryable<'Source> * System.Linq.Expressions.Expression<Func<'Source, 'Key>> * System.Collections.Generic.IComparer<'Key> -> System.Linq.IOrderedQueryable<'Source>
<Extension()>
Public Function ThenByDescending(Of TSource, TKey) (source As IOrderedQueryable(Of TSource), keySelector As Expression(Of Func(Of TSource, TKey)), comparer As IComparer(Of TKey)) As IOrderedQueryable(Of TSource)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TKey

keySelector 函数返回的键的类型。The type of the key that is returned by the keySelector function.

参数

source
IOrderedQueryable<TSource>

一个包含要排序的元素的 IOrderedQueryable<T>An IOrderedQueryable<T> that contains elements to sort.

keySelector
Expression<Func<TSource,TKey>>

用于从每个元素中提取键的函数。A function to extract a key from each element.

comparer
IComparer<TKey>

用于比较键的 IComparer<T>An IComparer<T> to compare keys.

返回

一个集合,其中的元素是根据某个键按降序进行排序的。A collection whose elements are sorted in descending order according to a key.

例外

sourcekeySelectorcomparernullsource or keySelector or comparer is null.

示例

下面的代码示例演示如何使用 ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) 通过使用自定义比较器按降序对序列中的元素执行次要排序。The following code example demonstrates how to use ThenByDescending<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) to perform a secondary ordering of the elements in a sequence in descending order by using a custom comparer.

public class CaseInsensitiveComparer : IComparer<string>
{
    public int Compare(string x, string y)
    {
        return string.Compare(x, y, true);
    }
}

public static void ThenByDescendingEx1()
{
    string[] fruits = 
    { "apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE" };

    // Sort the strings first ascending by their length and 
    // then descending using a custom case insensitive comparer.
    IEnumerable<string> query =
        fruits.AsQueryable()
        .OrderBy(fruit => fruit.Length)
        .ThenByDescending(fruit => fruit, new CaseInsensitiveComparer());

    foreach (string fruit in query)
        Console.WriteLine(fruit);
}

/*
    This code produces the following output:

    apPLe
    apple
    APple
    apPLE
    orange
    ORANGE
    baNanA
    BAnana
*/

Class CaseInsensitiveComparer
    Implements IComparer(Of String)

    Function Compare(ByVal x As String, ByVal y As String) As Integer _
        Implements IComparer(Of String).Compare

        ' Compare values and ignore case.
        Return String.Compare(x, y, True)
    End Function
End Class

Sub ThenByDescendingEx1()
    Dim fruits() As String = _
        {"apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE"}

    ' Sort the strings first ascending by their length and 
    ' then descending by using a custom case insensitive comparer.
    Dim query = fruits.AsQueryable() _
        .OrderBy(Function(fruit) fruit.Length) _
        .ThenByDescending(Function(fruit) fruit, New CaseInsensitiveComparer())

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

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

' This code produces the following output:

' apPLe
' apple
' APple
' apPLE
' orange
' ORANGE
' baNanA
' BAnana

注解

此方法至少具有一个类型 Expression<TDelegate> 的参数,其类型参数为 Func<T,TResult> 类型之一。This method has at least one parameter of type Expression<TDelegate> whose type argument is one of the Func<T,TResult> types. 对于这些参数,可以传入 lambda 表达式,并将其编译为 Expression<TDelegate>For these parameters, you can pass in a lambda expression and it will be compiled to an Expression<TDelegate>.

ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) 方法生成一个 MethodCallExpression,它表示作为构造的泛型方法调用 ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) 本身。The ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) method generates a MethodCallExpression that represents calling ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) itself as a constructed generic method. 然后,它将 MethodCallExpression 传递到 IQueryProviderCreateQuery<TElement>(Expression) 方法(由 source 参数的 Provider 属性表示)。It then passes the MethodCallExpression to the CreateQuery<TElement>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter. 调用 CreateQuery<TElement>(Expression) 的结果将强制转换为类型 IOrderedQueryable<T> 并返回。The result of calling CreateQuery<TElement>(Expression) is cast to type IOrderedQueryable<T> and returned.

因执行表示调用 ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) 的表达式树而发生的查询行为取决于 source 参数类型的实现。The query behavior that occurs as a result of executing an expression tree that represents calling ThenBy<TSource,TKey>(IOrderedQueryable<TSource>, Expression<Func<TSource,TKey>>, IComparer<TKey>) depends on the implementation of the type of the source parameter. 预期的行为是根据通过对每个 source元素调用 keySelector 获取的键,按降序对 source 的元素执行次要排序。The expected behavior is that it performs a secondary sort of the elements of source in descending order, based on the key obtained by invoking keySelector on each element of source. 所有以前建立的排序顺序都将保留。All previously established sort orders are preserved. comparer 参数用于比较键值。The comparer parameter is used to compare key values.

适用于