我可以在 LINQ 投影中捕获异常吗？

发布于 2024-11-02 05:25:54 字数 765 浏览 0 评论 0原文

假设我编写了一个 linq 查询，以获取有关 C 驱动器上隐藏文件的信息：

var q2 =
    from c in Directory.EnumerateFiles("C:\\")
    where Regex.IsMatch(c, @"^C:\\\.")
    select c;

var q3 =
    from c in q2
    let info = new 
    {
        File = c,
        FileSecurity = File.GetAccessControl(c),
        FileAttributes = File.GetAttributes(c),
        CreatedUTC = File.GetCreationTimeUtc(c),
        AccessedUTC = File.GetLastAccessTimeUtc(c),
        ModifiedUTC = File.GetLastWriteTimeUtc(c)
    }
    select info;

上面是一个逻辑示例，当捕获异常时，该逻辑可能希望继续执行，但我不知道如何在本例中实现这一点C# 编程风格（或者如果可能的话）。

从概念上讲，我想要某种“继续”语句，可以将其放入围绕 LINQ 查询的 catch 块的主体中。

try
{
   // LINQ QUERY
}
catch(Exception ex)
{
  Logger.Log("error...");
  continue;
}

原文

Say I write a linq query for info about the hidden files on my C drive:

var q2 =
    from c in Directory.EnumerateFiles("C:\\")
    where Regex.IsMatch(c, @"^C:\\\.")
    select c;

var q3 =
    from c in q2
    let info = new 
    {
        File = c,
        FileSecurity = File.GetAccessControl(c),
        FileAttributes = File.GetAttributes(c),
        CreatedUTC = File.GetCreationTimeUtc(c),
        AccessedUTC = File.GetLastAccessTimeUtc(c),
        ModifiedUTC = File.GetLastWriteTimeUtc(c)
    }
    select info;

The above is an example of logic that might want to keep going when an exception is caught, but I don't know how to get that to happen in this style of C# programming (or if its possible).

Conceptually I want some kind of "continue" statement that can be put in the body of a catch block surrounding a LINQ query.

try
{
   // LINQ QUERY
}
catch(Exception ex)
{
  Logger.Log("error...");
  continue;
}

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独木成林 2024-11-09 05:25:54

由于 LINQ 的惰性本质，您可能需要在开始使用迭代器时而不是在构建查询时进行尝试/捕获：

var q3 = ...

try
{
    foreach (var item in q3)
    {
        ...
    }
} 
catch(Exception ex)
{

}

Directory.EnumerateFiles 仅返回一个 IEnumerable 并且在开始之前不会进行任何评估迭代它。

更新：

为了避免在抛出异常时跳出循环，您可以执行以下操作：

static void Main()
{
    var q = Enumerable.Range(1, 5).Select(x =>
    {
        if (x % 2 == 0)
        {
            throw new Exception();
        }
        return x;
    });

    using (var enumerator = q.GetEnumerator())
    {
        while (true)
        {
            try
            {
                bool hasNext = enumerator.MoveNext();
                if (!hasNext)
                {
                    break;
                }

                Console.WriteLine(enumerator.Current);
            }
            catch (Exception ex)
            {
                // TODO: do something with the exception here
            }
        }
    }
}

Due to the lazy nature of LINQ you might need to try/catch when you start consuming the iterator and not when building the query:

var q3 = ...

try
{
    foreach (var item in q3)
    {
        ...
    }
} 
catch(Exception ex)
{

}

The Directory.EnumerateFiles simply returns an IEnumerable<string> and no evaluation happens until you start iterating over it.

UPDATE:

To avoid breaking out of the loop if an exception is thrown you could do the following:

static void Main()
{
    var q = Enumerable.Range(1, 5).Select(x =>
    {
        if (x % 2 == 0)
        {
            throw new Exception();
        }
        return x;
    });

    using (var enumerator = q.GetEnumerator())
    {
        while (true)
        {
            try
            {
                bool hasNext = enumerator.MoveNext();
                if (!hasNext)
                {
                    break;
                }

                Console.WriteLine(enumerator.Current);
            }
            catch (Exception ex)
            {
                // TODO: do something with the exception here
            }
        }
    }
}

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