MongoDB aggregate - filter by subdocument

Question

I have a mongodb collection with structure like that:

[
  {
    name: "name1",
    instances: [{value:1, score:2}, {value:2, score:5}, {value:2.5, score:9}]
  },
  {
    name: "name2",
    instances: [{value:6, score:3}, {value:1, score:6}, {value:3.7, score:5.2}]
  }
]

When I want to get all the data from a document, I use aggregate because I want each instance returned as a separate document:

db.myCollection.aggregate([{$match:{name:"name1"}}, {$unwind:"$instances"}, {$project:{name:1, value:"$instances.value", score:"$instances.score"}}])

And everything works like I want it to.

Now for my question: I want to filter the returned data by score or by value. For example, I want an array of all the subdocuments of name1 which have a value greater or equal to 2. I tried to add to the $match object 'instances.value':{$gte:2}, but it didn't filter anything, and I still get all 3 documents for this query.

Any ideas?

Help me to understand your problem clearly, do you have a sample expected output? — chridam
– chridam, Commented Apr 14, 2015 at 7:43
@chridam, expected result: [{name:"name1", value:2, score:5}, {name:"name1", value:2.5, score:9}] — Yaron Schwimmer
– Yaron Schwimmer, Commented Apr 14, 2015 at 7:47

Neo-coder · Accepted Answer · 2015-04-14 07:47:49Z

2

After unwinding instances then again used $match as below

    db.collectionName.aggregate({
    "$match": {
    "name": "name1"
    }
}, {
    "$unwind": "$instances"
}, {
    "$match": {
    "instances.value": {
        "$gte": 2
    }
    }
}, {
    $project: {
    name: 1,
    value: "$instances.value",
    score: "$instances.score"
    }
})

Or if you tried $match after project then used as below

 db.collectionName.aggregate([{
     $match: {
     name: "name1"
     }
 }, {
     $unwind: "$instances"
 }, {
     $project: {
     name: 1,
     value: "$instances.value",
     score: "$instances.score"
     }
 }, {
     "$match": {
     "value": {
         "$gte": 2
     }
     }
 }])

edited Apr 14, 2015 at 7:47

answered Apr 14, 2015 at 7:41

Neo-coder

7,8585 gold badges36 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

MongoDB aggregate - filter by subdocument

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related