Integer problems and countermeasures when operating MongoDB with PHP_PHP tutorial

本文所说的PHP-138" target=_blank>整数问题，其实并不是MongoDB的问题，而是PHP驱动的问题：MongoDB本身有两种整数类型，分别是：32位整数和64位整数，但旧版的PHP驱动不管操作系统是32位还是64位，把所有整数都当做32位整数处理，结果导致64位整数被截断。为了在尽可能保持兼容性的前提下解决这个问题，新版PHP驱动加入了mongo.native-long选项，以期在64位操作系统中把整数都当做64位来处理，有兴趣的可参考：html" target=_blank>64-bit integers in MongoDB。

那么PHP驱动真的完全解决了整数问题么？NO！在处理group操作的时候还有BUG：

为了说明问题，我们先来生成一些测试数据：

<font face="新宋体"><?php<BR><BR>ini_set(mongo.native_long, 1);<BR><BR>$instance = new Mongo();<BR><BR>$instance = $instance->selectCollection(test, test);<br><br>for ($i = 0; $i < 10; $i++) {<BR> $instance->insert(array(<br>        group_id => rand(1, 5),<br>        count    => rand(1, 5),<br>    ));<br>}<br><br>?></font>

下面让我们使用group操作，根据group_id分组，汇总计算count：

<font face="新宋体" size="2"><?php<BR><BR>ini_set(mongo.native_long, 1);<BR><BR>$instance = new Mongo();<BR><BR>$instance = $instance->selectCollection(test, test);<br><br>$keys = array(group_id => 1);<br><br>$initial = array(count => 0);<br><br>$reduce = <br>    function(obj, prev) {<br>        prev.count += obj.count;<br>    }<br>;<br><br>$result = $instance->group($keys, $initial, $reduce);<br><br>var_dump($result);<br><br>?></font>

结果和预想的有出入，count没有实现累加，而是变成了［object Object］，目前，如果必须使用group操作，那么有两种方法可以缓解这个问题：

<font face="新宋体" size="2">ini_set(mongo.native_long, 0);</font>

<font face="新宋体" size="2">$initial = array(count => (float)0);</font>

Both of these methods are expedient measures that treat the symptoms rather than the root cause. Since there is a problem with the implementation of group in the current PHP driver, we will bypass it and use other methods to achieve the same function. This method is MapReduce:

<font face="新宋体" size="2"><?php<BR><BR>ini_set(mongo.native_long, 1);<BR><BR>$instance = new Mongo();<BR><BR>$instance = $instance->selectDB(test);<br><br>$map = <br>    function() {<br>        emit(this.group_id, this.count);<br>    }<br>;<br><br>$reduce = <br>    function(key, values) {<br>        var sum = 0;<br><br>        for (var index in values) {<br>            sum += values[index];<br>        }<br><br>        return sum;<br>    }<br>;<br><br>$result = $instance->command(array(<br>    mapreduce => test,<br>    map       => $map,<br>    reduce    => $reduce<br>));<br><br>$result = iterator_to_array($instance->{$result[result]}->find());<br><br>var_dump($result);<br><br>?></font>

<font face="新宋体" size="2"><?php<BR><BR>ini_set(mongo.native_long, 1);<BR><BR>$instance = new Mongo();< BR><BR>$instance = $instance->selectDB(test);<br><br>$map = <br> function() {<br> emit(this.group_id, this.count);<br> }<br>;<br><br>$reduce = <br> function(key, values) {<br> var sum = 0;<br><br> for (var index in values) {<br> sum += values[index];<br> }<br><br> return sum;<br> }<br>;<br><br>$result = $instance->command(array(<br> mapreduce => test,<br> map => $map,<br> reduce => $reduce<br>));<br><br>$result = iterator_to_array($instance->{$result [result]}->find());<br><br>var_dump($result);<br><br>?></font>

It takes three steps to put an elephant in the refrigerator, but using MapReduce only requires two steps, Map and Reduce. Here is a PDF document that vividly illustrates the corresponding relationship between GROUP BY in MySQL and MapReduce in MongoDB:

SQL to MongoDB

In addition, there are many materials for reference, such as: MongoDB Aggregation III: Map-Reduce Basics

.

Note: The software version is MongoDB (1.6.5), PECL Mongo (1.1.4). The conclusions may be different in different versions.

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The PHP-138" target=_blank> integer problem mentioned in this article is actually not a MongoDB problem, but PHP driver problem: MongoDB itself has two integer types, namely: 32-bit integer and 6...