紧接着上篇来，这篇主要讲，mongodb的group功能，做的还是挺强大的，相当对于find()，skip()，distinct()等，用法比较复杂。
测试数据：
> db.fruit.find();
{ "_id" : 1, "category" : "fruit", "name" : "apple" }
{ "_id" : 2, "category" : "fruit", "name" : "peach" }
{ "_id" : 3, "category" : "fruit", "name" : "banana" }
{ "_id" : 4, "category" : "veggie", "name" : "corn" }
{ "_id" : 5, "category" : "veggie", "name" : "broccoli" }
</div>
1、根据category分组
> db.fruit.group(
{
key: { category: 1},
reduce: function(obj, prev) {
prev.items.push(obj.name);
},
initial: { items : [] }
}
);
[
{
"category" : "fruit",
"items" : [
"apple",
"peach",
"banana"
]
},
{
"category" : "veggie",
"items" : [
"corn",
"broccoli"
]
}
]
</div>
php代码如下：
$keys = array("category" => 1);
$initial = array("items" => array());
$reduce = "function (obj, prev) { prev.items.push(obj.name); }";
$g = $collection->group($keys, $initial, $reduce);
print_r($g); //结果如下。
Array
(
[retval] => Array
(
[0] => Array
(
[category] => fruit
[items] => Array
(
[0] => apple
[1] => peach
[2] => banana
)
)
[1] => Array
(
[category] => veggie
[items] => Array
(
[0] => corn
[1] => broccoli
)
)
)
[count] => 5
[keys] => 2
[ok] => 1
)
</div>
2、根据category来分组，并统计count
> db.fruit.group(
{
key: { category: 1},
cond: { _id: