MongoDB query to find and extract value from array

Question

I want to extract value from array. right now i have

db.getCollection('typeE').distinct("list.name",{"list.name":"C"})

I have such structure

object(1)"list":[{"name":"A","value":10},{"name":"B","value":20},{"name":"C","value":50}]
object(2)"list":[{"name":"D","value":100},{"name":"E","value":70}]

I want to receive 50 , but right now receive only object(1)

I also tried

db.getCollection('typeE').distinct("list.value",{"list": {$elemMatch: {"name":"C"}}})

but it's return array

felix · Accepted Answer · 2017-07-11 13:00:22Z

1

your doing this the wrong way. What you want (if I get you right) is to get distinct value of subdocuments having "name": "C"

you should try this :

db.getCollection('typeE').aggregate([
  {$unwind: "$list"},
  {$match: { "list.name": "C"}},
  {$group: {_id: null, distinctValue: {$addToSet: "$list.value"}}}
])

this will output:

{"_id": null, "distinctValue": [ 50 ] }

answered Jul 11, 2017 at 13:00

felix

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