The MongoDB itself has two integer types: 32-bit integers and 64-bit integers, but the older PHP driver, regardless of the operating system's 32-bit or 64-bit, treats all integers as 32-bit integers, resulting in 64-bit integers being truncated. In order to solve this problem with as much compatibility as possible, the new PHP driver joins the Mongo.native-longoption to treat all integers as 64 bits in a 64-bit operating system, with an interest in reference to: 64-bit integers in MongoDB。
So does the PHP driver really solve the integer problem completely? No! There are also bugswhen working with group operations:
To illustrate the problem, let's start by generating some test data:
Copy Code code as follows:
<?php
Ini_set (' Mongo.native_long ', 1);
$instance = new Mongo ();
$instance = $instance->selectcollection (' Test ', ' test ');
for ($i = 0; $i < $i + +) {
$instance->insert Array (
' group_id ' => rand (1, 5),
' Count ' => rand (1, 5),
));
}
?>
Let's use the group action, grouped by group_id, to summarize the count:
Copy Code code as follows:
<?php
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 results are not the same as expected, and the count does not accumulate, but instead becomes [object], and now if you must use group operations, there are two ways to mitigate this problem:
Copy Code code as follows:
Ini_set (' Mongo.native_long ', 0);
$initial = Array (' Count ' => (float) 0);
Both approaches are stopgap measures, and since there is a problem with the implementation of group in the current PHP driver, let's go around it and implement the same function in other ways, which is MapReduce：
Copy Code code as follows:
<?php
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 an elephant in the fridge, and using mapreduce requires only map and reduce two steps, and here's a PDF document that graphically illustrates the correspondence between group by and MongoDB in MySQL:
SQL to MongoDB
In addition, there are a lot of information available for reference, such as:MongoDB Aggregation iii:map-reduce Basics.
Description: The software version is MongoDB (1.6.5), PECL Mongo (1.1.4). Different versions may have different conclusions.
