本文译自：Create Youtube-like IDs with PHP/Python/Javascript/Java/SQL
id通常都是用数字，不巧的是只有10个数字来使用，所以如果你有很多的记录，id往往变得非常冗长。当然对于计算机来说无所谓，但我们更希望id尽可能短。所以我们如何能使id变短？我们可以利用字母让它们附加上数字。字母可以解决!
所以这里就有两个问题：
- 如何使用PHP和MySQL创建独特的短字符串id？
- 或如何创建id类似YouTube的方式，如yzNjIBEdyww？
我很久以前创建了这个函数。是时候和大家分享一下了。
多就是少 – “这就是数学”
字母有26个字母。这是一个已经超过10字数。如果我们还区分大写和小写字母,并添加数字,我们已经有(26 x 2 + 10)=62个选项我们可以使用，让它出现在我们的id中。
当然我们现在也可以添加其他特殊字符如：/ * & #，但是那些可能导致的URL上的一些问题。
因为大约有60+字符，让id变的更短，所以我们有更多的选择可以使数据在每个位置。
这就是因为网址必须做的更加短，就像youtube上看到的：http://www.youtube.com/watch?v=yzNjIBEdyww
转化你的id
不同于数据库服务器，网络服务容易收录这样的字符，这样你就可以让做一个转换id和字符串,同时保持你的数据库的快速与数字(MySQL真正喜欢它们纯数字);
由此产生的字符串不是很难破译, 但它可以是一个非常不错的功能使url或目录结构更紧凑的和更重要。
所以基本上:
- 当有人请求rLHWfKd
- alphaID()将其转换为999999999999
- 你查找的记录id 999999999999在你的数据库
PHP方式
/**
* Translates a number to a short alhanumeric version
*
* Translated any number up to 9007199254740992
* to a shorter version in letters e.g.:
* 9007199254740989 --> PpQXn7COf
*
* specifiying the second argument true, it will
* translate back e.g.:
* PpQXn7COf --> 9007199254740989
*
* this function is based on any2dec && dec2any by
* fragmer[at]mail[dot]ru
* see: http://nl3.php.net/manual/en/function.base-convert.php#52450
*
* If you want the alphaID to be at least 3 letter long, use the
* $pad_up = 3 argument
*
* In most cases this is better than totally random ID generators
* because this can easily avoid duplicate ID's.
* For example if you correlate the alpha ID to an auto incrementing ID
* in your database, you're done.
*
* The reverse is done because it makes it slightly more cryptic,
* but it also makes it easier to spread lots of IDs in different
* directories on your filesystem. Example:
* $part1 = substr($alpha_id,0,1);
* $part2 = substr($alpha_id,1,1);
* $part3 = substr($alpha_id,2,strlen($alpha_id));
* $destindir = "/".$part1."/".$part2."/".$part3;
* // by reversing, directories are more evenly spread out. The
* // first 26 directories already occupy 26 main levels
*
* more info on limitation:
* - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372
*
* if you really need this for bigger numbers you probably have to look
* at things like: http://theserverpages.com/php/manual/en/ref.bc.php
* or: http://theserverpages.com/php/manual/en/ref.gmp.php
* but I haven't really dugg into this. If you have more info on those
* matters feel free to leave a comment.
*
* The following code block can be utilized by PEAR's Testing_DocTest
* <code>
* // Input //
* $number_in = 2188847690240;
* $alpha_in = "SpQXn7Cb";
*
* // Execute //
* $alpha_out = alphaID($number_in, false, 8);
* $number_out = alphaID($alpha_in, true, 8);
*
* if ($number_in != $number_out) {
* echo "Conversion failure, ".$alpha_in." returns ".$number_out." instead of the ";
* echo "desired: ".$number_in."\n";
* }
* if ($alpha_in != $alpha_out) {
* echo "Conversion failure, ".$number_in." returns ".$alpha_out." instead of the ";
* echo "desired: ".$alpha_in."\n";
* }
*
* // Show //
* echo $number_out." => ".$alpha_out."\n";
* echo $alpha_in." => ".$number_out."\n";
* echo alphaID(238328, false)." => ".alphaID(alphaID(238328, false), true)."\n";
*
* // expects:
* // 2188847690240 => SpQXn7Cb
* // SpQXn7Cb => 2188847690240
* // aaab => 238328
*
* </code>
*
* @author Kevin van Zonneveld <[email protected]>
* @author Simon Franz
* @author Deadfish
* @copyright 2008 Kevin van Zonneveld (http://kevin.vanzonneveld.net)
* @license http://www.opensource.org/licenses/bsd-license.php New BSD Licence
* @version SVN: Release: $Id: alphaID.inc.php 344 2009-06-10 17:43:59Z kevin $
* @link http://kevin.vanzonneveld.net/
*
* @param mixed $in String or long input to translate
* @param boolean $to_num Reverses translation when true
* @param mixed $pad_up Number or boolean padds the result up to a specified length
* @param string $passKey Supplying a password makes it harder to calculate the original ID
*
* @return mixed string or long
*/
function alphaID($in, $to_num = false, $pad_up = false, $pass_key = null)
{
$out = '';
$index = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$base = strlen($index);
if ($pass_key !== null) {
// Although this function's purpose is to just make the
// ID short - and not so much secure,
// with this patch by Simon Franz (http://blog.snaky.org/)
// you can optionally supply a password to make it harder
// to calculate the corresponding numeric ID
for ($n = 0; $n < strlen($index); $n++) {
$i[] = substr($index, $n, 1);
}
$pass_hash = hash('sha256',$pass_key);
$pass_hash = (strlen($pass_hash) < strlen($index) ? hash('sha512', $pass_key) : $pass_hash);
for ($n = 0; $n < strlen($index); $n++) {
$p[] = substr($pass_hash, $n, 1);
}
array_multisort($p, SORT_DESC, $i);
$index = implode($i);
}
if ($to_num) {
// Digital number <<-- alphabet letter code
$len = strlen($in) - 1;
for ($t = $len; $t >= 0; $t--) {
$bcp = bcpow($base, $len - $t);
$out = $out + strpos($index, substr($in, $t, 1)) * $bcp;
}
if (is_numeric($pad_up)) {
$pad_up--;
if ($pad_up > 0) {
$out -= pow($base, $pad_up);
}
}
} else {
// Digital number -->> alphabet letter code
if (is_numeric($pad_up)) {
$pad_up--;
if ($pad_up > 0) {
$in += pow($base, $pad_up);
}
}
for ($t = ($in != 0 ? floor(log($in, $base)) : 0); $t >= 0; $t--) {
$bcp = bcpow($base, $t);
$a = floor($in / $bcp) % $base;
$out = $out . substr($index, $a, 1);
$in = $in - ($a * $bcp);
}
}
return $out;
}
还有一个可选的第三个参数:$pad_up。这能使生成的alphaId至少X字符长。
你可以支持更多字符(使生成的alphaID甚至更小)通过添加和修改函数顶部的$index变量。
Javascript方式
/**
* Javascript AlphabeticID class
* (based on a script by Kevin van Zonneveld <[email protected]>)
*
* Author: Even Simon <[email protected]>
*
* Description: Translates a numeric identifier into a short string and backwords.
*
* Usage:
* var str = AlphabeticID.encode(9007199254740989); // str = 'fE2XnNGpF'
* var id = AlphabeticID.decode('fE2XnNGpF'); // id = 9007199254740989;
**/
var AlphabeticID = {
index:'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ',
/**
* [@function](http://twitter.com/function) AlphabeticID.encode
* [@description](http://twitter.com/description) Encode a number into short string
* [@param](http://twitter.com/param) integer
* [@return](http://twitter.com/return) string
**/
encode:function(_number){
if('undefined' == typeof _number){
return null;
} else if('number' != typeof(_number)){
throw new Error('Wrong parameter type');
}
var ret = '';
for(var i=Math.floor(Math.log(parseInt(_number))/Math.log(AlphabeticID.index.length));i>=0;i--){
ret = ret + AlphabeticID.index.substr((Math.floor(parseInt(_number) / AlphabeticID.bcpow(AlphabeticID.index.length, i)) % AlphabeticID.index.length),1);
}
return ret.reverse();
},
/**
* [@function](http://twitter.com/function) AlphabeticID.decode
* [@description](http://twitter.com/description) Decode a short string and return number
* [@param](http://twitter.com/param) string
* [@return](http://twitter.com/return) integer
**/
decode:function(_string){
if('undefined' == typeof _string){
return null;
} else if('string' != typeof _string){
throw new Error('Wrong parameter type');
}
var str = _string.reverse();
var ret = 0;
for(var i=0;i<=(str.length - 1);i++){
ret = ret + AlphabeticID.index.indexOf(str.substr(i,1)) * (AlphabeticID.bcpow(AlphabeticID.index.length, (str.length - 1) - i));
}
return ret;
},
/**
* [@function](http://twitter.com/function) AlphabeticID.bcpow
* [@description](http://twitter.com/description) Raise _a to the power _b
* [@param](http://twitter.com/param) float _a
* [@param](http://twitter.com/param) integer _b
* [@return](http://twitter.com/return) string
**/
bcpow:function(_a, _b){
return Math.floor(Math.pow(parseFloat(_a), parseInt(_b)));
}
};
/**
* [@function](http://twitter.com/function) String.reverse
* [@description](http://twitter.com/description) Reverse a string
* [@return](http://twitter.com/return) string
**/
String.prototype.reverse = function(){
return this.split('').reverse().join('');
};
其他语言请参照原文：
http://kvz.io/blog/2009/06/10/create-short-ids-with-php-like-youtube-or-tinyurl/
