.NET Short Unique Identifier

Question

I need a unique identifier in .NET (cannot use GUID as it is too long for this case).

Do people think that the algorithm used here is a good candidate or do you have

Answer 1

var ticks = new DateTime(2016,1,1).Ticks;
var ans = DateTime.Now.Ticks - ticks;
var uniqueId = ans.ToString("x");

Keep a baseline date (which in this case is 1st Jan 2016) from when you will start generating these ids. This will make your ids smaller.

Generated Number: 3af3c14996e54

Answer 2

I know it's quite far from posted date... :)

I have a generator which produces only 9 Hexa characters, eg: C9D6F7FF3, C9D6FB52C

public class SlimHexIdGenerator : IIdGenerator
{
    private readonly DateTime _baseDate = new DateTime(2016, 1, 1);
    private readonly IDictionary<long, IList<long>> _cache = new Dictionary<long, IList<long>>();

    public string NewId()
    {
        var now = DateTime.Now.ToString("HHmmssfff");
        var daysDiff = (DateTime.Today - _baseDate).Days;
        var current = long.Parse(string.Format("{0}{1}", daysDiff, now));
        return IdGeneratorHelper.NewId(_cache, current);
    }
}


static class IdGeneratorHelper
{
    public static string NewId(IDictionary<long, IList<long>> cache, long current)
    {
        if (cache.Any() && cache.Keys.Max() < current)
        {
            cache.Clear();
        }

        if (!cache.Any())
        {
            cache.Add(current, new List<long>());
        }

        string secondPart;
        if (cache[current].Any())
        {
            var maxValue = cache[current].Max();
            cache[current].Add(maxValue + 1);
            secondPart = maxValue.ToString(CultureInfo.InvariantCulture);
        }
        else
        {
            cache[current].Add(0);
            secondPart = string.Empty;
        }

        var nextValueFormatted = string.Format("{0}{1}", current, secondPart);
        return UInt64.Parse(nextValueFormatted).ToString("X");
    }
}

Answer 3

As far as I know, just stripping off a part of a GUID isn't guaranteed to be unique - in fact, it's far from being unique.

The shortest thing that I know that guarantees global uniqueness is featured in this blog post by Jeff Atwood. In the linked post, he discusses multiple ways to shorten a GUID, and in the end gets it down to 20 bytes via Ascii85 encoding.

However, if you absolutely need a solution that's no longer than 15 bytes, I'm afraid you have no other choice than to use something which is not guaranteed to be globally unique.

Answer 4

Just in case merely removing hyphens will do for anyone:

Guid.NewGuid().ToString("n")

This generates perfectly unique strings of 32 characters:

5db4cee3bfd8436395d37fca2d48d5b3
82fac271c76148a3a0667c00a5da990d

Answer 5

you can use

code = await UserManager.GenerateChangePhoneNumberTokenAsync(input.UserId, input.MobileNumber);

its 6 nice characters only, 599527 ,143354

and when user virify it simply

var result = await UserManager.VerifyChangePhoneNumberTokenAsync(input.UserId, input.Token, input.MobileNumber);

hope this help you