MongoDB find by max value in array of documents

Question

Given a collection with documents such as:

{
    "host" : "example.com",
    "ips" : [
        {
            "ip" : NumberLong("1111111111"),
            "timestamp" : NumberLong(1373970044)
        },
        {
            "ip" : NumberLong("2222222222"),
            "timestamp" : NumberLong(1234978746)
        }
    ]
}

I need to return all documents with an ip value of X, but only if the associated timestamp for X is the highest timestamp in the ips array (so the above example document should not match a search for "2222222222" because that is not the IP with the most recent timestamp).

This is my first time doing anything much beyond fairly basic stuff in MongoDB so the closest I've been able to get is:

coll.aggregate({$match:{"ips.ip":X}},{$group:{"_id":"$host", "max":{$max:"$ips.timestamp"}}},{$sort:{"ips.timestamp":-1}}).result

Which obviously doesn't give me what I'm looking for, it returns anything with an ips.ip value of X. How do I return only documents where ip.ip is X only if X's associated timestamp is the highest for that ips array?

score 16 · Accepted Answer · edited Apr 05 '20 at 11:43

16

If host is unique, the following code should do the job. Otherwise, you can simply replace host by _id in the grouping operation:

coll.aggregate([
  {$unwind: "$ips"},
  {$project:{host:"$host",ip:"$ips.ip", ts:"$ips.timestamp"} },
  {$sort:{ts:1} },
  {$group: {_id: "$host", IPOfMaxTS:{$last: "$ip"}, ts:{$last: "$ts"} } }
])

edited Apr 05 '20 at 11:43

Xavier Guihot

54,987
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answered Jul 18 '13 at 23:19

innoSPG

4,588
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42

Disregard above comment, I was on the right track I just foolishly put the match in the wrong place, placing `$match:{"IPOfMaxTS":X}}` _after_ the group operation gives me exactly what I was looking for. Thanks for the help! – frostmatthew Jul 19 '13 at 15:06
2

Thanks, this $unwind function worked for a similar problem for me. – Tom Swifty Oct 24 '13 at 14:03

score 1 · Answer 2 · answered Jan 21 '19 at 15:09

you can use $reduce in aggregation pipeline starting from mongo 3.4 version

db.t64.aggregate([
    {$addFields : {ips : {$reduce : {
        input : "$ips", 
        initialValue : {timestamp : 0}, 
        in : {$cond: [{$gte : ["$$this.timestamp", "$$value.timestamp"]},"$$this", "$$value"]}}
    }}}
])

sample collection

> db.t64.findOne()
{
        "_id" : ObjectId("5c45e00f328877e101354d97"),
        "host" : "example.com",
        "ips" : [
                {
                        "ip" : NumberLong(1111111111),
                        "timestamp" : NumberLong(1373970044)
                },
                {
                        "ip" : NumberLong("2222222222"),
                        "timestamp" : NumberLong(1234978746)
                }
        ]
}

output

> db.t64.aggregate([ {$addFields : {ips : {$reduce : { input : "$ips",  initialValue : {timestamp : 0},  in : {$cond: [{$gte : ["$$this.timestamp", "$$value.timestamp"]},"$$this", "$$value"]}} }}} ])
{ "_id" : ObjectId("5c45e00f328877e101354d97"), "host" : "example.com", "ips" : { "ip" : NumberLong(1111111111), "timestamp" : NumberLong(1373970044) } }

score 0 · Answer 3 · answered Apr 27 '17 at 08:16

IN Simple Words , if you have mongo query Response something like below - and you want only highest value from Array-> "Date"

{
  "_id": "57ee5a708e117c754915a2a2",
  "TotalWishs": 3,
  "Events": [
    "57f805c866bf62f12edb8024"
  ],
  "wish": [
    "Cosmic Eldorado  Mountain Bikes, 26-inch (Grey/White)",
    "Asics Men's Gel-Nimbus 18 Black, Snow and Fiery Red Running Shoes - 10 UK/India (45 EU) (11 US)",
    "Suunto Digital Black Dial Unisex Watch - SS018734000"
  ],
  "Date": [
    "2017-02-13T00:00:00.000Z",
    "2017-03-05T00:00:00.000Z"
  ],
  "UserDetails": [
    {
      "createdAt": "2016-09-30T12:28:32.773Z",
      "jeenesFriends": [
        "57edf8a96ad8f6ff453a384a",
        "57ee516c8e117c754915a26b",
        "58a1644b6c91d2af783770b0",
        "57ef4631b97d81824cf54795"
      ],
      "userImage": "user_profile/Male.png",
      "email": "roopak@small-screen.com",
      "fullName": "Roopak Kapoor"
    }
  ],

},

***Then you have add

Latest_Wish_CreatedDate: { $max: "$Date"},

somthing like below-

{ 
                $project : { _id: 1,
                             TotalWishs : 1 ,
                              wish:1 ,
                               Events:1, 
                               Wish_CreatedDate:1,
                               Latest_Wish_CreatedDate: { $max: "$Date"},
                            } 
            }

And Final Query Response will be below

{
  "_id": "57ee5a708e117c754915a2a2",
  "TotalWishs": 3,
  "Events": [
    "57f805c866bf62f12edb8024"
  ],
  "wish": [
    "Cosmic Eldorado  Mountain Bikes, 26-inch (Grey/White)",
    "Asics Men's Gel-Nimbus 18 Black, Snow and Fiery Red Running Shoes - 10 UK/India (45 EU) (11 US)",
    "Suunto Digital Black Dial Unisex Watch - SS018734000"
  ],
  "Wish_CreatedDate": [
    "2017-03-05T00:00:00.000Z",
    "2017-02-13T00:00:00.000Z"
  ],
  "UserDetails": [
    {
      "createdAt": "2016-09-30T12:28:32.773Z",
      "jeenesFriends": [
        "57edf8a96ad8f6ff453a384a",
        "57ee516c8e117c754915a26b",
        "58a1644b6c91d2af783770b0",
        "57ef4631b97d81824cf54795"
      ],
      "userImage": "user_profile/Male.png",
      "email": "roopak@small-screen.com",
      "fullName": "Roopak Kapoor"
    }
  ],
  "Latest_Wish_CreatedDate": "2017-03-05T00:00:00.000Z"
},

MongoDB find by max value in array of documents

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