Mongodb query documents where nested array is equal or subset of fixed array

Question

I keep banging my head against the wall trying to solve the following problem (I'm using the new c# 2.0 driver):

The idea is to return all docs where the nested array is equal or a subset of a fixed array. Example:

Fixed array: [ "A", "B", "C" ]

container docs:

{
    container1 { Name: "name1", Tags: [ "A", "B" ] },
    container2 { Name: "name4", Tags: [ "A", "B", "C", "D" ] },
    container3 { Name: "name2", Tags: [ "A" ] },
    container4 { Name: "name3", Tags: [ "A", "B", "C" ] }
}

Based on the above data, the result should be:

{
    container1 { Name: "name1", Tags: [ "A", "B" ] },
    container3 { Name: "name2", Tags: [ "A" ] },
    container4 { Name: "name3", Tags: [ "A", "B", "C" ] }
}

Notice how container2 was not part of the result set since [ "A", "B", "C", "D" ] is not a subset nor equal to [ "A", "B", "C" ]

Please if you have a non-2.0-C#-driver solution post it here anyways. It will help.

Much appreciated!!!

Answer 1

Use mongo Set Operator using $setIsSubset in aggregation you will get your result, check following query :

db.collectionName.aggregate({
  "$project": {
    "Name": 1,
    "Tags": 1,
    "match": {
      "$setIsSubset": ["$Tags", ["A", "B", "C"]] //check Tags is subset of given array in your case array is ["A","B","C"]
    }
  }
}, {
  "$match": {
    "match": true // return only those matched true values
  }
}, {
  "$project": {
    "Name": 1,
    "Tags": 1
  }
}).pretty()