Mongodb sum all the same fields in array foreach document - Map-Reduce

Question

I have documents like this in my db:

{
"first_name": "John",
"last_name": "Bolt",
"account": [
  {
    "cardnumber": "4844615935257045",
    "cardtype": "jcb",
    "currency": "CZK",
    "balance": 4924.99
  },
  {
    "cardnumber": "3552058835710041",
    "cardtype": "jcb",
    "currency": "BRL",
    "balance": 9630.38
  },
  {
    "cardnumber": "5108757163721629",
    "cardtype": "visa-electron",
    "currency": "CNY",
    "balance": 6574.18
  }
}

And my question is - how can I sum balances for all accounts foreach person separately? Should I use for this Map-Reduce or Aggregation Framework?

Community · Accepted Answer · 2017-05-23 12:21:55Z

3

Use the aggregation framework.

This will give you an array of objects with two properties, id and balance where id contains the user's name.

db.document.aggregate([{
  $unwind: "$account"
}, {
  $group: {
    _id: {$concat: [ "$first_name", " ", "$last_name" ]},
    "balance": {
      $sum: "$account.balance"
    }
  }
}]);

Disclaimer: untested.

Ps: I sure hope that's dummy information. Here's another answer that might prove helpful.

edited May 23, 2017 at 12:21

CommunityBot

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answered May 18, 2015 at 0:08

Amin Shah Gilani

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2 Comments

saltwat5r Over a year ago

Thanks for your response, but I want to get a list of all separated people with sum of all balances for each of them - not a sum of total balances of all people.

Amin Shah Gilani Over a year ago

Ohh, no, the query gave you the sum of all balances specifically for John Bolt. Here, i've updated the query in the answer.

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