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POGuid.NewGuid() VS a random string generator from Random.Next()
 

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  1. POGuid.NewGuid() VS a random string generator from Random.Next()
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    <p>My colleague and I are debating which of these methods to use for auto generating user ID's and post ID's for identification in the database:</p> <p>One option uses a single instance of Random, and takes some useful parameters so it can be reused for all sorts of string-gen cases (i.e. from 4 digit numeric pins to 20 digit alphanumeric ids). Here's the code:</p> <pre><code>// This is created once for the lifetime of the server instance class RandomStringGenerator { public const string ALPHANUMERIC_CAPS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"; public const string ALPHA_CAPS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; public const string NUMERIC = "1234567890"; Random rand = new Random(); public string GetRandomString(int length, params char[] chars) { string s = ""; for (int i = 0; i &lt; length; i++) s += chars[rand.Next() % chars.Length]; return s; } } </code></pre> <p>and the other option is simply to use:</p> <pre><code>Guid.NewGuid(); </code></pre> <p>see <a href="http://msdn.microsoft.com/en-us/library/system.guid.newguid.aspx">Guid.NewGuid on MSDN</a></p> <p>We're both aware that <code>Guid.NewGuid()</code> would work for our needs, but I would rather use the custom method. It does the same thing but with more control.</p> <p>My colleague thinks that because the custom method has been cooked up ourselves, it's more likely to generate collisions. I'll admit I'm not fully aware of the implementation of Random, but I presume it is just as random as Guid.NewGuid(). A typical usage of the custom method might be:</p> <pre><code>RandomStringGenerator stringGen = new RandomStringGenerator(); string id = stringGen.GetRandomString(20, RandomStringGenerator.ALPHANUMERIC_CAPS.ToCharArray()); </code></pre> <p><strong>Edit 1:</strong></p> <ul> <li>We are using Azure Tables which doesn't have an auto increment (or similar) feature for generating keys.</li> <li>Some answers here just tell me to use NewGuid() "because that's what it's made for". I'm looking for a more in depth reason as to why the cooked up method may be more likely to generate collisions given the same degrees of freedom as a Guid.</li> </ul> <p><strong>Edit 2:</strong></p> <p>We were also using the cooked up method to generate post ID's which, unlike session tokens, need to look pretty for display in the url of our website (like <a href="http://mywebsite.com/14983336">http://mywebsite.com/14983336</a>), so guids are not an option here, however collisions are still to be avoided.</p>
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    1. USGeorge Powell
    1. USGeorge Powell
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      1. USO. R. Mapper
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    1. CO`Random` makes *NO* guarantee of uniqueness. It is perfectly valid for a random sequence to contain the same result multiple times.
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      1. USGalacticCowboy
    2. COIf you cook it up yourself, it is less likely to be **UNIQUE** then a GUID. A GUID makes use of certain hardware factors and the current time to generate a particular GUID. You can research the details yourself. A GUID won't be unique if you hit the same GUID generator too often in a short segment of time. Again, you can look up the details yourself.
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      1. USStarPilot
    3. COIf you want to generate unique user IDs and post IDs, you should use auto-incrementing numbers from a database. Hit the database, get back the next number in that sequence. Guaranteed unique.
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