如何使用一致的语法重写此LINQ表达式？

Question

This one-statement query says neatly "Give me a list of bare filenames for which the file is a ZIP repository containing a certain file structure."

But I use both a .Where() extension method (fluent syntax) and a select query, because anything else I try fails to compile. If I change ".Where(file ==> <statement>)" to "where <statement>", I get an error that the anonymous method code does not return a bool, and if I change the "select <clause>" to ".Select(<clause>)", the error is "No select clause is used."

I'm happy with either query or fluent syntax, but I'd like to settle on one or the other. Can anyone explain why this does not work, and what I would need to do to settle on one consistent syntax?

return (from file in Directory.EnumerateFiles(
                    Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData), Globals.CompanyName, ProjectName, FolderName),
                    imageExtension,
                    SearchOption.TopDirectoryOnly)
    .Where(file =>
    {
        try
        {
            string relativePath = ClassFru.Station + "/";   // Inside ZIPs, paths use a single forward slash
            var zip = new ZipFile();
            zip.ZipError += (s, o) => { throw new Exception(); };
            using (zip = ZipFile.Read(file))
            {
                /// <todo>if (zip.Comment != Globals.CompanyName) { return false; }</todo>
                foreach (var fru in this.gFrus)
                {
                    var fruPath = relativePath + fru.Id + '.';
                    if (!(from e in zip where !e.IsDirectory && e.FileName.StartsWith(fruPath) select true).Any()) { return false; }
                }
                return true;
            }
        }
        catch (Exception)
        {
            return false;
        }
    })
    select Path.GetFileNameWithoutExtension(file)).ToArray();

Answer 1

Since I don't have all type you're using in this expression it's quite hard to compile it but I think i should work like that:

            return (Directory.EnumerateFiles(
            Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData),
                Globals.CompanyName, ProjectName, FolderName),
            imageExtension,
            SearchOption.TopDirectoryOnly)
            .Where(file => {
                try
                {
                    string relativePath = ClassFru.Station + "/"; // Inside ZIPs, paths use a single forward slash
                    var zip = new ZipFile();
                    zip.ZipError += (s, o) => {
                        throw new Exception();
                    };
                    using (zip = ZipFile.Read(file))
                    {
                        /// <todo>if (zip.Comment != Globals.CompanyName) { return false; }</todo>
                        foreach (var fru in this.gFrus)
                        {
                            var fruPath = relativePath + fru.Id + '.';
                            if(zip.Any(e=> !e.IsDirectory && e.FileName.StartsWith(fruPath))
                                    .Any())
                            {
                                return false;
                            }
                        }
                        return true;
                    }
                } catch (Exception)
                {
                    return false;
                }
            }).Select(Path.GetFileNameWithoutExtension).ToArray());

Answer 2

除了将select的使用更改为Select(file =>你还需要在开始时删除from file in 。然后你将删除使用那个查询语法select子句。这是单独from子句导致你看到的错误。 from [...] in子句中的每个都需要匹配的select 。

Answer 3

I'm happy with either query or fluent syntax, but I'd like to settle on one or the other. Can anyone explain why this does not work, and what I would need to do to settle on one consistent syntax?

It's not working very well for you because LINQ was not really made to handle large blocks of complex logic as criteria. LINQ Expression syntax, in particular, makes the assumption that you are going to provide Expressions (not Blocks), so it doesn't directly support multi-line statements.

If you simply remove the from portion of your query, you can easily get method syntax to work, as ISun shows you how to do .

On the other hand, your code will be much more understandable and modular if you simply extract your anonymous method out, as @Servy suggested in comments. In that case, you could either decide to say where FileHasMatchingZipStructure(file) . or .Where(FileHasMatchingZipStructure) , as you like.