Mongodb compare two fields with matched fields value aggregate

问题

I am having problems in my query, The parameter I am passing are voucherId, and userId, I need to check if that user exceeded the limitedQuantityPerUser. If yes, exclude this voucher. But I am having problems comparing the matching fields, example if voucherId is 'aaa', check if the quantityBrought > limitedQuantityPerUser.

I have tried this

vouchers.find({
         'status': {
          $in: ['OP', 'WG', 'LO', 'SO']
        },
        'details.userReachedLimitedQuantity': {
          $ne: userId
        },
      }, fields, {
        sort: {
          'order': 1
        }
      }

But this will give me all the result where userId not equal in the list. not exactly what I need. Is it better to solve using aggregate?

Example resource JSON file

[{
        "_id": "111",
        "details": {
            "limitedQuantityPerUser": "3",
            "userReachedLimitedQuantity": [{
                    "userId": "aaa",
                    "quantityBrought": "2"
                },
                {
                    "userId": "bbb",
                    "quantityBrought": "1"
                },
                {
                    "userId": "ccc",
                    "quantityBrought": "3"
                }
            ],
            "status": "OP"
        }
    },
    {
        "_id": "222",
        "details": {
            "limitedQuantityPerUser": "2",
            "userReachedLimitedQuantity": [{
                    "userId": "eee",
                    "quantityBrought": "2"
                },
                {
                    "userId": "bbb",
                    "quantityBrought": "1"
                },
                {
                    "userId": "vvv",
                    "quantityBrought": "2"
                }
            ],
            "status": "OP"
        }
    }
]

回答1:

You can use below aggregation to check whether specified userId exceeded defined limit.

db.vouchers.aggregate([
    {
        $match: {
            $expr: {
                $allElementsTrue: {
                    $map: {
                        input: "$details.userReachedLimitedQuantity",
                        as: "user",
                        in: {
                            $or: [
                                { $ne: [ "$$user.userId", userId ] },
                                { $lte: [ "$$user.quantityBrought", "$details.limitedQuantityPerUser"  ] }
                            ]
                        }
                    }
                }
            }
        }
    }
])

$allElementsTrue takes an array of boolean values as a parameter. You can use $map to transform your userReachedLimitedQuantity into such boolean values checking userId and quantityBrought fields.

So if any element is false then it means that that user's quantityBrought is greater than limitedQuantityPerUser

回答2:

No a perfect answer, but I did the filter in the result of mongod query

// Only take matched userId's quantityPurchased
const newResult = result.filter(val => {
  if (!val.details.userReachedLimitedQuantity) {
    return val;
  }
  val.details.userReachedLimitedQuantity= val.details.userReachedLimitedQuantity.filter((o) => {
    return (String(o.userId) == userId)
  });
  if (val.details.userReachedLimitedQuantity[0].quantityBrou < val.details.limitedQuantityPerUser) {
    return val;
  } else {
    return false;
  }

来源：https://stackoverflow.com/questions/53995878/mongodb-compare-two-fields-with-matched-fields-value-aggregate

标签

mongodb

aggregation-framework