C# LINQ 中的条件“orderby”排序顺序
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/1606454/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Conditional "orderby" sort order in LINQ
提问by xyz
In LINQ, is it possible to have conditional orderby sort order (ascending vs. descending).
在 LINQ 中，是否可以有条件 orderby 排序顺序（升序与降序）。
Something like this (not valid code):
像这样（无效代码）：
bool flag;
(from w in widgets
where w.Name.Contains("xyz")
orderby w.Id (flag ? ascending : descending)
select w)
采纳答案by Richard
If you build the expression incrementally you can do this. Generally easier using expressions rather than comprehension expressions:
如果您逐步构建表达式，则可以执行此操作。通常更容易使用表达式而不是理解表达式：
var x = widgets.Where(w => w.Name.Contains("xyz"));
if (flag) {
x = x.OrderBy(w => w.property);
} else {
x = x.OrderByDescending(w => w.property);
}
(Assuming the Widget's propertyis basis of sort since you don't list one.)
（假设 Widgetproperty是排序的基础，因为您没有列出一个。）
回答by Konamiman
You can define a base query without the ordering, then order according to the flag:
您可以定义一个没有排序的基本查询，然后根据标志进行排序：
var query=(from w in widgets
where w.Name.Contains("xyz")
select w);
var result = flag ?
query.OrderBy(w =>w) :
query.OrderByDescending(w = w);
回答by cloggins
You could try something like the following:
您可以尝试以下操作：
var q = from i in list
where i.Name = "name"
select i;
if(foo)
q = q.OrderBy(o=>o.Name);
else
q = q.OrderByDescending(o=>o.Name);
回答by Carter Medlin
...Or do it all in one statement
...或者在一个声明中完成所有操作
bool flag;
var result = from w in widgets where w.Name.Contains("xyz")
orderby
flag ? w.Id : 0,
flag ? 0 : w.Id descending
select w;
回答by Julian Lettner
If the ordering property Idis a number (or supports the unary minus) one could also do:
如果 ordering 属性Id是一个数字（或支持一元减号），还可以这样做：
bool ascending = ...
collection.Where(x => ...)
.OrderBy(x => ascending ? x.Id : -x.Id)
.Select(x => ...)
// LINQ query
from x in ...
orderby (ascending ? x.Id : -x.Id)
select ...
回答by Julian Lettner
回答by Jezze
Here is a more general solution, that can be used for various conditional lambda expressions without breaking the flow of the expression.
这是一个更通用的解决方案，可用于各种条件 lambda 表达式，而不会中断表达式的流程。
public static IEnumerable<T> IfThenElse<T>(
this IEnumerable<T> elements,
Func<bool> condition,
Func<IEnumerable<T>, IEnumerable<T>> thenPath,
Func<IEnumerable<T>, IEnumerable<T>> elsePath)
{
return condition()
? thenPath(elements)
: elsePath(elements);
}
e.g.
例如
var result = widgets
.Where(w => w.Name.Contains("xyz"))
.IfThenElse(
() => flag,
e => e.OrderBy(w => w.Id),
e => e.OrderByDescending(w => w.Id));
回答by watbywbarif
You can even do more complex ordering and still keep it short:
您甚至可以进行更复杂的排序，但仍然保持简短：
var dict = new Dictionary<int, string>() { [1] = "z", [3] = "b", [2] = "c" };
var condition = true;
var result = (condition ? dict.OrderBy(x => x.Key) : dict.OrderByDescending(x => x.Value))
.Select(x => x.Value);
