Get array subset in mongodb using an array source

Question

I have this document's structure:

{
    Id: "id_value",
    Elements:[
                {
                    InnerId: "inner_id_value1",
                    Value: "apple"
                },
                {
                    InnerId: "inner_id_value2",
                    Value: "pear"
                },
                {
                    InnerId: "inner_id_value3",
                    Value: "banana"
                }
             ]
}

What i need to do is create a query which receives in input an array (for example ["apple","banana","coconut"] ) and returns to me:

{
    Id: "id_value",
    Elements:[
                {
                    InnerId: "inner_id_value1",
                    Value: "apple"
                },
                {
                    InnerId: "inner_id_value3",
                    Value: "banana"
                }
             ]
}

Is it possible do it in Mongo with a single query?

What is your MongoDB version?

Sede
– Sede

2016-09-29 15:35:38 +00:00
Commented Sep 29, 2016 at 15:35 — Sede
– Sede, Commented Sep 29, 2016 at 15:35
@Styvane version 3.2

Marco
– Marco

2016-09-29 15:36:46 +00:00
Commented Sep 29, 2016 at 15:36 — Marco
– Marco, Commented Sep 29, 2016 at 15:36

Sede · Accepted Answer · 2016-09-29 15:49:44Z

4

You simply need to $filter the array and keep only those subdocument where the value is a subset of your input array. Note that value here is one element array where element is the embedded field value.

let fruits = ["apple","banana","coconut"];

db.collection.aggregate([
    { "$project": { 
        "Element": { 
            "$filter": { 
                "input": "$Element", 
                "as": "el", 
                "cond": { 
                    "$setIsSubset": [ [ "$$el.Value" ], fruits ] 
                 }
            }
        }
    }}
])

Starting from MongoDB 3.4* you can use the $in operator in the $project stage.

db.collection.aggregate([
    { "$project": { 
        "Element": { 
            "$filter": { 
                "input": "$Element", 
                "as": "el", 
                "cond": { 
                    "$in": [ "$$el.Value", fruits ] 
                 }
            }
        }
    }}
])

_{*Unreleased version of MongoDB as the time of this writing}

edited Sep 29, 2016 at 15:49

answered Sep 29, 2016 at 15:43

Sede

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2 Comments

sudheeshix Over a year ago

$setIsSubset is new to me. Thanks! Just curious about the null set scenario, since it is a subset of every set - if $$el.Value is empty for a document, wont that also be included in this query result?

Sede Over a year ago

No it will not be included.

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