Bugs and Strategies for PHP Driver MongoDB Integer Issues_PHP Tutorial

The integer problem mentioned in this article is not actually a problem with MongoDB, but a problem with the PHP driver: MongoDB itself has two integer types, namely: 32-bit integer and 64-bit integer, but the old version of PHP Regardless of whether the operating system is 32-bit or 64-bit, the driver treats all integers as 32-bit integers, resulting in 64-bit integers being truncated. In order to solve this problem while maintaining compatibility as much as possible, the new version of the PHP driver has added the mongo.native-long option, in order to treat integers as 64-bit in 64-bit operating systems. Those who are interested can refer to: 64- bit integers in MongoDB.

So does the PHP driver really completely solve the integer problem? NO! There are still bugs when handling group operations:

To illustrate the problem, let’s first generate some test data:

ini_set('mongo.native_long', 1);

　$instance = new Mongo();

$instance = $instance->selectCollection('test', 'test');

　for ($i = 0; $i < 10; $i++) {

　$instance->insert(array(

　'group_id' => rand(1, 5),

　'count' => rand(1, 5),

　));

　}

　?>

Next let us use the group operation to group according to group_id and calculate the count in summary:

ini_set('mongo.native_long', 1);

　$instance = new Mongo();

$instance = $instance->selectCollection('test', 'test');

　$keys = array('group_id' => 1);

　$initial = array('count' => 0);

$reduce = '

Function(obj, prev) {

prev.count += obj.count;

　}

　;

$result = $instance->group($keys, $initial, $reduce);

var_dump($result);

　?>

The result is different from what was expected. Count did not accumulate, but became [object Object]. Currently, if group operations must be used, there are two methods to alleviate this problem:

ini_set('mongo.native_long', 0);

　$initial = array('count' => (float)0);

These two 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:

ini_set('mongo.native_long', 1);

　$instance = new Mongo();

$instance = $instance->selectDB('test');

$map = '

Function() {

emit(this.group_id, this.count);

　}

　;

$reduce = '

Function(key, values) {

　var sum = 0;

　for (var index in values) {

sum += values[index];

　}

return sum;

　}

　;

$result = $instance->command(array(

'mapreduce' => 'test',

'map' => $map,

'reduce' => $reduce

　));

　$result = iterator_to_array($instance->{$result['result']}->find());

var_dump($result);

　?>

It takes three steps to put the 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: