如何使用mongodb和jasper从对象列表中计算特定字段？

Question

我正在使用jasper服务器和mongodb创建报告。我的json如下：

{
  "_index": "spot",
  "_type": "events",
  "_id": "AVNVuep8N5qpVGQABmT3",
  "_score": null,
  "_source": {
    "eventType": "kioskTransaction",
    "messageType": "event",
    "version": "1",
    "timestamp": 1457432194130,
    **"data": {
      "amount": 4,
      "products": [
        {
          "bin": "6",
          "quantity_units": "Oz",
          "quantity": 2
        },
        {
          "bin": "3",
          "quantity_units": "Oz",
          "quantity": 2
        },
        {
          "bin": "4",
          "quantity_units": "Oz",
          "quantity": 2
        },
        {
          "bin": "CP1",
          "quantity_units": "CUP",
          "quantity": 1
        }
      ],**
      "payments": [
        {
          "last_four": "9142",
          "expiration_date": "0000",
          "troutd": "1410045878",
          "card_type": "Visa",
          "amount": 4,
          "invoice": "CM00006399",
          "type": "credit_card"
        }
      ],
      "language": "English"
    },
    "tzoffset": -8,
    "spotId": "SSN-CK-0332",
    "org": "/root/ssn/candyfactory",
    "spotTimestamp": 1457403713474,
    "spotTimezone": -8
  },
  "fields": {
    "spotTimestamp": [
      1457403713474
    ],
    "timestamp": [
      1457432194130
    ]
  },
  "sort": [
    "kiosktransaction"
  ]
}

当我尝试获取data.products时，我会得到如下列表：

{
  "bin": "6",
  "quantity_units": "Oz",
  "quantity": 2
},
{
  "bin": "3",
  "quantity_units": "Oz",
  "quantity": 2
},
{
  "bin": "4",
  "quantity_units": "Oz",
  "quantity": 2
},
{
  "bin": "CP1",
  "quantity_units": "CUP",
  "quantity": 1
}

但是在不计算机中没有可用的选项来计算每个箱子中的数量。如果你知道的话，请帮助我，因为我被卡住了。