C# Linq if/else 条件？

Linq if/else condition?

提问by Sparhawk

I know this will probably be a newbie question. Is there a way to choose different search criteria depending on the bool value? Later in the code, I want to loop through the object (alDisabledPrograms). I know the if/else is not correct, I put that in there to show how I'd like that to be handled. I attempted to place this inside a larger if/else condition but was unable to loop through alDisabledPrograms later. Thoughts?

我知道这可能是一个新手问题。有没有办法根据布尔值选择不同的搜索条件？在代码的后面，我想遍历对象 (alDisabledPrograms)。我知道 if/else 不正确，我把它放在那里以表明我希望如何处理它。我试图将它放在一个更大的 if/else 条件中，但后来无法通过 alDisabledPrograms 循环。想法？

var alDisabledPrograms = xlServerRoles.Descendants("ServerRole")
    if(isDup)
    {
        .Where(dp => dp.Element("ServerType").Value == currentColumn.Substring(0, currentColumn.Length - 1))
    }
    else
    {
        .Where(dp => dp.Element("ServerType").Value == currentColumn)
    }
    .Descendants("ProgramName")
    .Select(p => p.Value)
    .ToList();

采纳答案by Jon Skeet

With your particular code, the answer is really simple:

使用您的特定代码，答案非常简单：

string targetColumn = isDup ? currentColumn.Substring(0, currentColumn.Length - 1)
                            : currentColumn;
var alDisabledPrograms = xlServerRoles.Descendants("ServerRole")
           .Where(dp => dp.Element("ServerType").Value == targetColumn)
           .Descendants("ProgramName")
           .Select(p => p.Value)
           .ToList();

In general though, to apply very different queries, you could either use:

但总的来说，要应用非常不同的查询，您可以使用：

IEnumerable<XElement> roles = xlServerRoles.Descendants("ServerRole");
if (isDup)
{
    roles = roles.Where(dp => ...);
}
else
{
    roles = roles.Where(dp => ...);
}
var alDisabledPrograms = roles.Descendants(...)
                               ...

Or you could maybe use the conditional operator to construct the right predicate:

或者您可以使用条件运算符来构造正确的谓词：

var filter = isDup ? (Func<XElement, bool>)(dp => ...)
                   : (Func<XElement, bool>)(dp => ...);
var alDisabledPrograms = xlServerRoles.Descendants("ServerRole")
       .Where(filter)
       .Descendants("ProgramName")
       .Select(p => p.Value)
       .ToList();

回答by dthorpe

Move the isDup test into the Where expression itself. Use an inline annonymous function instead of a single line expression so that you can use a normal if/else statement.

将 isDup 测试移至 Where 表达式本身。使用内联匿名函数而不是单行表达式，以便您可以使用普通的 if/else 语句。

Like this:

像这样：

var alDisabledPrograms = xlServerRoles.Descendants("ServerRole")
        .Where(dp => { 
           if (isDup)
           {
             return dp.Element("ServerType").Value == currentColumn.Substring(0, currentColumn.Length - 1))
           }
           else
           {
              return dp.Element("ServerType").Value == currentColumn)
           })
    .Descendants("ProgramName")
    .Select(p => p.Value)
    .ToList();

回答by Casperah

Insert the isDup in the where clause:

在 where 子句中插入 isDup：

var alDisabledPrograms = xlServerRoles.Descendants("ServerRole")
     .Where(dp => isDup ? 
       (dp.Element("ServerType").Value == currentColumn.Substring(0, currentColumn.Length - 1)) : 
       (dp.Element("ServerType").Value == currentColumn))
    .Descendants("ProgramName")
    .Select(p => p.Value)
    .ToList();

I think this will do.

我认为这会做。

回答by Servy

Just do it once before the start of the loop:

只需在循环开始前执行一次：

string serverType = currentColumn;
if(isDup)
    serverType = currentColumn.Substring(0, currentColumn.Length - 1);

var alDisabledPrograms = xlServerRoles.Descendants("ServerRole")
    .Where(dp => dp.Element("ServerType").Value == serverType )
    .Descendants("ProgramName")
    .Select(p => p.Value)
    .ToList();

回答by outcoldman

You can construct query like this:

您可以像这样构造查询：

var query = xlServerRoles.Descendants("ServerRole");

if(isDup)
{
    query = query.Where(dp => dp.Element("ServerType").Value == currentColumn.Substring(0, currentColumn.Length - 1))
}
else
{
    query = query.Where(dp => dp.Element("ServerType").Value == currentColumn)
}

var alDisabledPrograms = query.Descendants("ProgramName").Select(p => p.Value).ToList();

回答by Kishore Kumar

Place you isDup inside Where

把你放在里面哪里

.Where(dp => dp.Element("ServerType").Value == (isDup ? currentColumn.Substring(0, currentColumn.Length - 1) 
                                                  : currentColumn))