上升/在LINQ降 - 可以在一个修改通过参数的顺序？ [英] ascending/descending in LINQ - can one change the order via parameter?

问题描述

我有被赋予参数布尔sortAscending的方法。现在我想使用LINQ创建根据此参数排序列表。我得到那么这个：

I have a method which is given the parameter "bool sortAscending". Now I want to use LINQ to create sorted list depending on this parameter. I got then this:

var ascendingQuery = from data in dataList
                      orderby data.Property ascending
                      select data;

var descendingQuery = from data in dataList
                      orderby data.Property descending
                      select data;

正如你可以看到，这两个查询只有在升序RESP不同。 降。我想合并这两个查询，但我不知道怎么办。 ？有没有人有答案

As you can see, both queries differ only in "ascending" resp. "descending". I'd like to merge both queries, but I don't know how. Does anyone have the answer?

推荐答案

您可以轻松地创建的IEnumerable或IQueryable的自己的扩展方法：

You can easily create your own extension method on IEnumerable or IQueryable:

public static IOrderedEnumerable<TSource> OrderByWithDirection<TSource,TKey>
    (this IEnumerable<TSource> source,
     Func<TSource, TKey> keySelector,
     bool descending)
{
    return descending ? source.OrderByDescending(keySelector)
                      : source.OrderBy(keySelector);
}

public static IOrderedQueryable<TSource> OrderByWithDirection<TSource,TKey>
    (this IQueryable<TSource> source,
     Expression<Func<TSource, TKey>> keySelector,
     bool descending)
{
    return descending ? source.OrderByDescending(keySelector)
                      : source.OrderBy(keySelector);
}

是的，你失去了在这里使用一个查询表达的能力 - 但坦白说，我不要以为你实际上是从查询表达式在这种情况下，受益反正。查询表达式是伟大的复杂的东西，但如果你只是做一个单一的操作很简单，只是把一个操作：

Yes, you lose the ability to use a query expression here - but frankly I don't think you're actually benefiting from a query expression anyway in this case. Query expressions are great for complex things, but if you're only doing a single operation it's simpler to just put that one operation:

var query = dataList.OrderByWithDirection(x => x.Property, direction);

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