How do I generate an ID that is garunteed to be unique?

Question

I need to garuntee the uniqueness of an ID. Even if there's a 1 in 1 trillion chance of there being a dupe, I cannot use it.

But I don't really feel like going to the ends of the earth to find a solution either. I have spent some time looking into this, and everything I have found to date isn't able to garuntee me a unique ID.

So I thought I would use something very simple, like this:

    public static string GenerateItemID()
    {
        string year = DateTime.Now.Year.ToString(), 
            month = DateTime.Now.Month.ToString(), 
            day = DateTime.Now.Day.ToString(), 
            hour = DateTime.Now.Hour.ToString(), 
            minute = DateTime.Now.Minute.ToString(), 
            second = DateTime.Now.Second.ToString(), 
            millisecond = DateTime.Now.Millisecond.ToString();

        return year + month + day + hour + minute + second + millisecond;
    }

My logic here is: each new UI that is generated can not possibly be the same as any of the previous ones. But then I wondered if it were possible for a PC to generate two or more of these ID's within the same millisecond? Naturally, I then looked in Intellisense for a Nanosecond property, but it doesn't exist.

How can I generate an ID that is garunteed to be unique?

Where did you manage to buy a processor that never produces an incorrect result? — CodesInChaos, Jul 05 '15 at 15:24

score 4 · Answer 1 · answered Jul 05 '15 at 14:22

4

var id = Guid.NewGuid();

I believe this will create a fairly unique id.

answered Jul 05 '15 at 14:22

George Harnwell

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Are GUID's _garunteed_ to _always_ be unique? I have read that there is still some margin for duplication. – SE13013 Jul 05 '15 at 14:23
I imagine there is 1 in a quadrillion chance or so. You could use a 'while' and say while (id is not unique) generate new guid? – George Harnwell Jul 05 '15 at 14:24
1

Guids will most likely be sufficient, check out this article for additional information: http://blogs.msdn.com/b/oldnewthing/archive/2008/06/27/8659071.aspx – Saragis Jul 05 '15 at 14:24
You could just add a random 8 digit number after your milliseconds. http://stackoverflow.com/questions/1344221/how-can-i-generate-random-alphanumeric-strings-in-c – TRose Jul 05 '15 at 14:25
Then add logic to retry to generate a new GUID should the one you try to insert fail... – Azmi Kamis Jul 05 '15 at 14:26
@TRose I was just thinking that! lol – SE13013 Jul 05 '15 at 14:26
@SE13013 added a link to an example. – TRose Jul 05 '15 at 14:27
@SE13013 No, they aren't (see http://stackoverflow.com/a/30919505/613130)... But they are guaranteed to be statistically unique (in the sense that the probability of a collision is so much low to be *truly* low...) – xanatos Jul 05 '15 at 14:28

score 2 · Answer 2 · answered Jul 05 '15 at 14:22

2

Let use GUID.

Refer here: https://msdn.microsoft.com/en-us/library/system.guid.newguid(v=vs.110).aspx

Hope this help.

answered Jul 05 '15 at 14:22

hungndv

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How do I generate an ID that is garunteed to be unique?

2 Answers2