CODE EXAMPLE FOR JAVASCRIPT

mongodb filter array

/**
Assume we have docs in MyCollection with the folowing structure:
{
	"users": [
    	{"name": "John", "age": 34},
        {"name": "Kate", "age": 17},
        {"name": "Simon", "age": 65},
        {"name": "Alice", "age": 27}
    ]
}
*/

db.MyCollection.aggregate([
  {
    "$project": {
      "users": {
        "$filter": {
          "input": "$users",
          "as": "user",
          "cond": {
            "$and": [
              {"$gte": ["$$user.age", 18]},
              {"$lte": ["$$user.age", 50]}
            ]
          }
        }
      }
  	}
  }
])

/**
This way we'll have the result
{
    "_id" : ObjectId("63690f75ccdacb91c24682f0"),
    "users" : [ 
        {
            "name" : "John",
            "age" : 34
        }, 
        {
            "name" : "Alice",
            "age" : 27
        }
    ]
}
*/