php - 如何获得MongoDB中两个字段的差异之和？

Question

我已经有了一个解决方案，但我正在寻找一个可以在 MongoServer 上完成所有工作的解决方案（因为我认为它会更快且内存消耗更少）

我有一个类方法，如：

function getTotalOutstandingAmount(){
    $outstandingAmount = 0;
    $subs = $this->mongo->selectCollection('SmsSubscriptions');
    $activeSubsctiptions = $subs->find(array('Status' => 1, '$where' => "this.SubscriptionPayments < this.SubscriptionTotal"));
    foreach ($activeSubsctiptions AS $sub){
        $outstandingAmount += $sub['SubscriptionTotal'] - $sub['SubscriptionPayments'];
    }

    return $outstandingAmount;
}

aggregate现在有没有一种方法可以使用MongoDB 的方法计算两个字段的差异之和？还有其他更有效的方法吗？

Answer 1

聚合方法应该有这个管道：

db.SmsSubscriptions.aggregate([
    { 
        "$project": {
            "outstandingAmount": { 
                "$subtract": ["$SubscriptionTotal", "$SubscriptionPayments"] 
            },
            "Status": 1
        }
    },
    { "$match": { "Status": 1, "outstandingAmount": { "$gt": 0 } } },   
    {
        "$group": {
            "_id": null,
            "totalOutstandingAmount": { "$sum": "$outstandingAmount" }
        }
    }
])

等效的 PHP 示例实现：

$ops = array(
    array(
        "$project" => array(
            "Status" => 1,
            "outstandingAmount" => array(               
                "$subtract" => array("$SubscriptionTotal", "$SubscriptionPayments")
                )
            )           
        )
    ),
    array( 
        "$match" => array( 
            "Status" => 1, 
            "outstandingAmount" => array("$gt" => 0) 
        ) 
    ),
    array(
        "$group" => array(
            "_id" => null,
            "totalOutstandingAmount" => array("$sum" => "$outstandingAmount" )
        )
    )
);
$results = $this->mongo->selectCollection('SmsSubscriptions')->aggregate($ops);

Answer 2

获得差异总和的通用简单紧凑解决方案

收藏X

{ _id: 'xxxx', itemOne: 100, itemTwo: 300 }

{ _id: 'yyyy', itemOne: 200, itemTwo: 800 }

{ _id: 'zzzz', itemOne: 50, itemTwo: 400 }

聚合操作

db.collectionX.aggregate([
  {
    $group: {
      _id: null,
      sumOfDifferences: { $sum: { $subtract: ['$itemTwo', '$itemOne']}
  }
])

回复

{
   "_id" : null,
   "sumOfDifferences" : 1150
}