MongoDB find in Arrays and objects with several nesting levels

Question

I try to match a document in this nested structure, it works for one level but not for the second level:

{
 type:"example"
 level1:[
          {
            name:"Bill"
            level2:[
                     {
                       skill:"gardening"
                     },
                     {
                       skill:"carpentry"
                     }
            ]

           },

          {
            name:"John"
            level2:[
                     {
                       skill:"painting"
                     },
                     {
                       skill:"acrobatics"
                     }
            ]

          }
        ]

}

I can match the first level array, for example:

db.collection.find({"level1.name":{$eq:"Bill"}})

But if for example I want to math the document with the skill field equal to "acrobatics" I do:

db.collection.find({"level1.level2.skill":{$eq:"acrobatics"}})

Does not work, any idea? (sorry if the naming of the example does not make much sense, but that's the structure that I'm facing).

Thank you!

exactly what was your question? query is not working or you need whole structure in result? you can update your question first. — turivishal
– turivishal, Commented Aug 13, 2020 at 9:57
It's returning the whole structure because the collection only has 1 document, which matches the query. — Rudey
– Rudey, Commented Aug 13, 2020 at 9:57
@Mapin you can project in find using $ check this mongoplayground.net/p/1hl2l3CGKPb — turivishal
– turivishal, Commented Aug 13, 2020 at 10:03
@varman yes you are right, this is helpful only in unique value, and for multiple match there is a only option is aggregation. — turivishal
– turivishal, Commented Aug 13, 2020 at 10:22

varman · Accepted Answer · 2020-08-13 10:15:37Z

1

There are multiple ways you can do this. You can try something like this.

$unwind to flatten the first level array
$match to match the element that you need
$group to group back to the same level

Shell query is given below

[
  {
    "$unwind": "$level1"
  },
  {
    $match: {
      "level1.level2.skill": "acrobatics"
    }
  },
  {
    "$group": {
      _id: "$_id",
      level1: {
        "$addToSet": "$level1"
      }
    }
  }
]

Working Mongo playground

edited Aug 13, 2020 at 10:15

answered Aug 13, 2020 at 9:59

varman

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3 Comments

Mapin Over a year ago

Thanks, I'll have to do pipelines for fast classification as well:)

varman Over a year ago

So you can easily do with $match stage.

turivishal Over a year ago

@varman you can use $push instead of $addToSet, because $addToSet will replace the same object, look mongoplayground.net/p/NKMZOvnrYlv

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