Orderby() not ordering numbers correctly c#

问题

I am writing an app for my company and am currently working on the search functionality. When a user searches for an item, I want to display the highest version (which is stored in a database).

The problem is, the version is stored as a string instead of int, and when I do an OrderBy(q=>q.Version) on the results, they are returned like

Obviously 2 comes before 10.

Is there a way for me to cast the version as an integer or is there a simple IComparer out there? I couldn't find anything substantial thus far.

I tried doing this:

var items = (from r in results
             select r).OrderBy(q => Int32.Parse(q.Version));

This compiles but doesn't work.

回答1:

Int32.Parse is not supported by the LinqToSql translator. Convert.ToInt32 is supported.

http://msdn.microsoft.com/en-us/library/sf1aw27b.aspx

http://msdn.microsoft.com/en-us/library/bb882655.aspx

回答2:

Your problem is somewhere else, the following works:

new[] { "1", "10", "2", "3", "11" }
    .OrderBy(i => int.Parse(i))
    .ToList()
    .ForEach(Console.WriteLine);

If your problem is LINQ to SQL, then what is happening is CLR is trying to create SQL out of your LINQ and doesn't understand int.Parse. What you can do is first get the data from SQL then order it once all data is loaded:

var items = (from r in results
             select r)
            .ToList()
            .OrderBy(q => Int32.Parse(q.Version));

Should do it.

回答3:

If you're unable to change your table definition (so the version is a numeric type), and your query really is as listed (your not using skip, or take, or otherwise reducing the number of results), the best you can do is call "ToList" on the unsorted results, which when you then apply an OrderBY lambda to it will take place in your code, rather than trying to do it at the SQL Server end (and which should now work).

回答4:

Why are you sorting in a lambda? Why don't you just sort in the query?

var query = from r in items
            orderby int.Parse( r )
            select r;

Now that we know you are using LINQ to SQL, you might consider making a standard SQL call on this one by doing something like:

Select ..., Cast( TextWhichShouldBeIntCol As int ) As IntCol
From ...

Or even

Select ..., Cast( TextWhichShouldBeIntCol As int ) As IntCol
From ...
Order By Cast( TextWhichShouldBeIntCol As int )

That will bleed into your LINQ as an int (and if you use the second iteration, be ordered). That avoids having to go through the resultset twice in LINQ (once for querying, once for ordering).

回答5:

There's an awesome piece of code that does a great job when it comes to natural sorting. Its name is AlphanumComparator.

Sample code:

var ordered = Database.Cars.ToList().OrderBy(c => c.ModelString, new AlphanumComparator());

Note that the list must be in memory.

If you get the C# version, do this:

AlphanumComparator : IComparer<string>

and

public int Compare(string x, string y)

回答6:

I made a test. I have the following code.

string[] versions = { "1", "2", "10", "12", "22", "30" };
foreach (var ver in versions.OrderBy(v => v))
{
     Console.WriteLine(ver);
}

As expected the result is 1, 10, 12, 2, 22, 30 Then lets change versions.OrderBy(v => v)) to versions.OrderBy(v => int.Parse(v))). And it works fine: 1, 2, 10, 12, 22, 30

I think your problem is that you have nondigit chars in your string like '.'. What kind of exception do you get?

回答7:

try this:

var items = results.(Select(v => v).OrderBy(v => v.PadLeft(4));

that'll work in Linq2Sql

回答8:

Why are you sorting if you only need "the highest version"? It sounds like you could avoid some overhead if you used Max().

Also, you really should change the column type to integer.

回答9:

var items = (from r in results
         select r).OrderBy(q => Convert.ToInt32(q.Version));

Definitely run......

回答10:

It sounds like you have a text value instead of a numeric value.

If you need to sort, you can try:

var items = (from r in results
             select r);
return items.OrderBy( v=> Int.Parse(v.Version) );

回答11:

var query = from r in items
            let n = int.Parse(r)
            orderby n
            select n;

回答12:

var items = (from v in results
                    select v).ToList().OrderBy(x => int.Parse(x.Version));

来源：https://stackoverflow.com/questions/2410070/orderby-not-ordering-numbers-correctly-c-sharp

标签

asp.net-mvc

linq

linq-to-sql

sql-order-by