创建一个唯一的 5 个字符的字母数字字符串

Question

我们正在考虑创建促销代码以发送给客户，我们被告知发送的每个代码必须是唯一的 - 5 个字符 - 字母数字。

我考虑过对连接的字符串进行散列处理并取散列的前 5 个字符，但很可能会一次又一次出现相同的 5 个字符。

任何人都可以给我任何关于创建这个每次都是唯一的 5 字符字母数字字符串的指示吗？

Answer 1

我不久前想到了这个，它可能会满足您的需求。

/// <summary>
/// Return a string of random hexadecimal values which is 6 characters long and relatively unique.
/// </summary>
/// <returns></returns>
/// <remarks>In testing, result was unique for at least 10,000,000 values obtained in a loop.</remarks>
public static string GetShortID()
{
    var crypto = new System.Security.Cryptography.RNGCryptoServiceProvider();
    var bytes = new byte[5];
    crypto.GetBytes(bytes); // get an array of random bytes.      
    return BitConverter.ToString(bytes).Replace("-", string.Empty); // convert array to hex values.
}

我理解您的要求是 "must" 是唯一的，但请记住，唯一性充其量只是一个相对概念。甚至我们的老朋友 the GUID 也不是 真正的 独一无二的:

...the probability of the same number being generated randomly twice is negligible

如果我没记错的话，我发现我的代码不是 100% 唯一的，只有 5 个字符经过许多次迭代（数十万次或可能低数百万次——我记不太清楚了），但在测试中对于 6，结果是对于在循环中获得的至少 10,000,000 个值是唯一的。

您可以在长度为 5 时自行测试并确定它是否足够独特以达到您的目的。如果需要，只需将 6 切换为 5。

附录： 其他一些提醒我您可能需要考虑线程安全。这是一种修改后的方法：

private static object _lock = new object();

/// <summary>
/// Return a string of random hexadecimal values which is 6 characters long and relatively unique.
/// </summary>
/// <returns></returns>
/// <remarks>In testing, result was unique for at least 10,000,000 values obtained in a loop.</remarks>
public static string GetShortID()
{
    lock(_lock)
    {
        var crypto = new System.Security.Cryptography.RNGCryptoServiceProvider();
        var bytes = new byte[5];
        crypto.GetBytes(bytes); // get an array of random bytes.      
        return BitConverter.ToString(bytes).Replace("-", string.Empty); // convert array to hex values.
    }
}

Answer 2

我会创建一个包含所有可能的 5 位字符串的 table (PromoCode)。然后用两个字段创建另一个 table CampaignPromoCode：

Code varchar(5), CampaignId uniqueidentifier

这样您就可以跟踪每个广告系列的使用情况。要获得随机未使用的促销代码，请使用此语句：

select top 1 Code 
from PromoCode pc
    left join CampaignPromoCode cpc on cpc.Code = pc.Code
where cpc.CampaignId = 'campaign-id-goes-here'
  and cpc.Code is null
order by newid()

Answer 3

这里的底线是，您可能应该回到管理层并告诉他们强制 100% 绝对唯一性的要求是一项成本过高的要求，您只需花费一小部分成本即可获得 99.9999% 的唯一性.然后使用 roryap 的代码生成一个随机的，主要是唯一的代码。

Answer 4

正如我在其他回答的评论中提到的，它可能不足以满足您的目的。我编写了更多代码来生成一串运行dom 字母数字字符。这一次，它们不限于 0-9 和 A-F——即运行domly 生成的 nibbles 的十六进制等价物。相反，它们由完整的运行ge 字母数字字符组成，至少是大写字母。这应该足以增加唯一性的可能性，因为我们从 16 个可能的十六进制字符到 36 个可能的完整字母和 0-9 字符。

不过，当我运行尝试超过 10,000,000 次时，还是出现了很多重复项。这只是野兽的本性：你用这么短的字符串被骗的可能性相当高。无论如何，它就在这里。你可以玩弄它。如果您的客户不介意小写字母——例如如果 "RORYAP" 与 "RoryAp" 不同——那么这甚至会进一步增加唯一性的可能性。

/// <summary>
/// Instances of this class are used to geneate alpha-numeric strings.
/// </summary>
public sealed class AlphaNumericStringGenerator
{
    /// <summary>
    /// The synchronization lock.
    /// </summary>
    private object _lock = new object();

    /// <summary>
    /// The cryptographically-strong random number generator.
    /// </summary>
    private RNGCryptoServiceProvider _crypto = new RNGCryptoServiceProvider();

    /// <summary>
    /// Construct a new instance of this class.
    /// </summary>
    public AlphaNumericStringGenerator()
    {
        //Nothing to do here.
    }

    /// <summary>
    /// Return a string of the provided length comprised of only uppercase alpha-numeric characters each of which are
    /// selected randomly.
    /// </summary>
    /// <param name="ofLength">The length of the string which will be returned.</param>
    /// <returns>Return a string of the provided length comprised of only uppercase alpha-numeric characters each of which are
    /// selected randomly.</returns>
    public string GetRandomUppercaseAlphaNumericValue(int ofLength)
    {
        lock (_lock)
        {
            var builder = new StringBuilder();

            for (int i = 1; i <= ofLength; i++)
            {
                builder.Append(GetRandomUppercaseAphanumericCharacter());
            }

            return builder.ToString();
        }
    }

    /// <summary>
    /// Return a randomly-generated uppercase alpha-numeric character (A-Z or 0-9).
    /// </summary>
    /// <returns>Return a randomly-generated uppercase alpha-numeric character (A-Z or 0-9).</returns>
    private char GetRandomUppercaseAphanumericCharacter()
    {
            var possibleAlphaNumericValues =
                new char[]{'A','B','C','D','E','F','G','H','I','J','K','L',
                'M','N','O','P','Q','R','S','T','U','V','W','X','Y',
                'Z','0','1','2','3','4','5','6','7','8','9'};

            return possibleAlphaNumericValues[GetRandomInteger(0, possibleAlphaNumericValues.Length - 1)];
    }

    /// <summary>
    /// Return a random integer between a lower bound and an upper bound.
    /// </summary>
    /// <param name="lowerBound">The lower-bound of the random integer that will be returned.</param>
    /// <param name="upperBound">The upper-bound of the random integer that will be returned.</param>
    /// <returns> Return a random integer between a lower bound and an upper bound.</returns>
    private int GetRandomInteger(int lowerBound, int upperBound)
    {
        uint scale = uint.MaxValue;

        // we never want the value to exceed the maximum for a uint, 
        // so loop this until something less than max is found.
        while (scale == uint.MaxValue)
        {
            byte[] fourBytes = new byte[4];
            _crypto.GetBytes(fourBytes); // Get four random bytes.
            scale = BitConverter.ToUInt32(fourBytes, 0); // Convert that into an uint.
        }

        var scaledPercentageOfMax = (scale / (double) uint.MaxValue); // get a value which is the percentage value where scale lies between a uint's min (0) and max value.
        var range = upperBound - lowerBound;
        var scaledRange = range * scaledPercentageOfMax; // scale the range based on the percentage value
        return (int) (lowerBound + scaledRange);
    }
}

创建一个唯一的 5 个字符的字母数字字符串

Create a UNIQUE 5 character alphanumeric string

c#

string

alphanumeric

promotion-code