为什么我通过linq订购不起作用

Question

Trying to order logs by logtype or by logType and thenBy DateTime but does not work.What am I missing?

      public enum LogType
    {
        Fatal,
        Error,
        Warn,
        Info,
        Debug,
        None,
    }
    public class Log
    {
        public DateTime LoggedDateTime { get; set; }
        public string Message { get; set; }
        public LogType LoggedType { get; set; }
        public override string ToString()
        {
            return string.Format("LogType: {0} Datetime: {1} Message: {2}", LoggedType, LoggedDateTime, Message);
        }
    }
    class Program
    {
        static void Main()
        {
            var logFatal = new Log
                               {
                                   LoggedDateTime = new DateTime(2011, 2, 22),
                                   Message = "Hi am a Fatal message",
                                   LoggedType = LogType.Fatal
                               };

            var logInfo = new Log
            {
                LoggedDateTime = new DateTime(2013, 2, 22),
                Message = "Hi I am a Info message",
                LoggedType = LogType.Info
            };

            var logError = new Log
            {
                LoggedDateTime = new DateTime(2010, 2, 22),
                Message = "Hi I am a Error message",
                LoggedType = LogType.Error
            };

            var logWarning = new Log
            {
                LoggedDateTime = new DateTime(2014, 2, 22),
                Message = "Hi I am a Warning message",
                LoggedType = LogType.Warn
            };
            List<Log> logs = new List<Log> { logWarning, logError, logInfo, logFatal };

            Console.WriteLine("Not Ordered");
            Console.WriteLine("");
            logs.ForEach(x=>Console.WriteLine(x.LoggedType));



            var orderedLogs = logs.OrderBy(x => x.LoggedType == LogType.Fatal)
                .ThenBy(x => x.LoggedType == LogType.Error)
                .ThenBy(x => x.LoggedType == LogType.Warn)
                .ThenBy(x => x.LoggedDateTime).ToList();

            Console.WriteLine("Ordered by logType fatal first and NOT WORKING");
            Console.WriteLine("");

            orderedLogs.ForEach(x=>Console.WriteLine(x.LoggedType));

            Console.WriteLine("");
            Console.WriteLine("Ordered by logType fatal first and NOT WORKING");//NOT WORKING
            List<Log> orderedFatal = logs.OrderBy(x => x.LoggedType == LogType.Fatal).ToList();
            orderedFatal.ForEach(x => Console.WriteLine(x.LoggedType));

            Console.WriteLine("");
            Console.WriteLine("Sorted by datetime AND WORKS"); //THIS IS THE ONLY ONE THAT WORKS
            logs.Sort((x,y)=>x.LoggedDateTime.CompareTo(y.LoggedDateTime));
            logs.ForEach(x => Console.WriteLine(x.LoggedDateTime));


            Console.Read();
        }
    }

Thanks for any suggestions

Answer 1

The problem is that false is ordered before true . Thus first in your order come those that are not Fatal. Out of those first come those that are not Error etc.

You can use inequalities to make it work:

x => x.LoggedType != LogType.Fatal

etc.

or use OrderByDescending and ThenByDescending .

But I'd prefer to give an order of the enum:

public enum LogType : int
    {
        Fatal = 5,
        Error = 4,
        Warn = 3,
        Info = 2,
        Debug = 1,
        None = 0,
}

and then just use this value:

var orderedLogs = logs.OrderByDescending(x => x.LoggedType);

Answer 2

Both your logWarning and logError have LoggedType = LogType.Error !

Another point: you should implement/use an IComparer for LogType ... see MSDN at http://msdn.microsoft.com/en-us/library/8ehhxeaf.aspx

Bascially something like:

public class LogComparer : IComparer<Log>
{
    public int Compare(Log x, Log y)
    {
        if ( x == y ) return 0;
        if ( x.LoggedType == y.LoggedType ) return 0;
        if ( x.LoggedType == LogType.Fatal ) return 1;
        if ( y.LoggedType == LogType.Fatal ) return -1;
        // etc.
    }
}

// Usage similar to this
logs.OrderBy(x => x, new LogComparer());

Answer 3

You need to do something like:

var orderedLogs = logs.GroupBy(l => l.LoggedType)
                    .OrderBy(g => g.Key)
                    .SelectMany(g => g.OrderByDescending(l => l.LoggedDateTime)).ToList();

Answer 4

You can sort the collection by the field LoggedType, then by the field LoggedDateTime in the following code:

var orderedLogs = logs.OrderBy(x => x.LoggedType) // not x => x.LoggedType == LogType.Fatal
    .ThenBy(x => x.LoggedDateTime).ToList();

I think there will be sorting by integer representation of enum. So with your enum there will be Fatal, Error, Warn etc. Or you can use IComparer (from Yahia answer) for your own definition rules of comparison.