How to return Objects with empty sub Array document if sub Array documents don't satisfy the match condition?

Question

Mongoose is not returning Objects if sub Array documents don't satisfy the match condition in mongoose.

MongoDB Query:

db.fruits.aggregate(        
    { $match: { "isActive": true, fruitId: "kipld" } },
    { $unwind: '$types' },
    { $match: { "types.isActive": true } },
    { $group: {
            _id: '$_id', 
            name: {$first: '$name'}, 
            price: { $first: '$price' },
            types : { $push : '$types' }
        }
    },
    { $project: {
            '_id': 1, 
            'name':1, 
            'price': 1, 
            'types': 1,
        }
    }
)

MongoDB Collection:

{
    _id: "abcdefg",
    fruitId: "kipld",
    isActive: true,
    types :[
        {
            name: "Kashmir Apple",
            price: 90,
            isActive: false
        },
        {
            name: "American Apple",
            price: 120,
            isActive: false
        }
    ]
}

Expected result will be like:

{
    _id: "abcdefg",
    fruitId: "kipld",
    isActive: true,
    types :[]
}

But when I'm running the above query I'm not getting anything.

Your query says `{ $match: { "types.isActive": true } }`, but the input document has `"tyoes.isActive"` values as `false`. So, no documents get selected. — prasad_, Oct 14 '19 at 07:16
can I do that to return `EMPTY` array if there are no `true` records present? — Rajath, Oct 14 '19 at 07:31
You can check here: https://stackoverflow.com/questions/3985214/retrieve-only-the-queried-element-in-an-object-array-in-mongodb-collection — Cuong Le Ngoc, Oct 14 '19 at 07:39
@Rajath You can. But, not with that query pipeline you are using. — prasad_, Oct 14 '19 at 07:41

prasad_ · Accepted Answer · 2019-10-14T10:28:03.800

You can get the desired result using the $filter aggregation operator. This just filters all the array elements and returns the array with the matching filter condition. Note the filter is applied to each document's array. So, in your case the $unwind and $group stages are not needed to get the result.

Sample fruits collection:

{
        "_id" : "abcdefg",
        "fruitId" : "kipld",
        "isActive" : true,
        "types" : [
                {
                        "name" : "Kashmir Apple",
                        "price" : 90,
                        "isActive" : false
                },
                {
                        "name" : "American Apple",
                        "price" : 120,
                        "isActive" : false
                }
        ]
}
{
        "_id" : "uvwxyz",
        "fruitId" : "kipld",
        "isActive" : true,
        "types" : [
                {
                        "name" : "Kinnaur Apple",
                        "price" : 80,
                        "isActive" : false
                },
                {
                        "name" : "Shimla Apple",
                        "price" : 70,
                        "isActive" : true
                }
        ]
}

Aggregation Query:

db.fruits.aggregate([
  { $match: { "isActive": true, fruitId: "kipld" } },
  { $project: { _id: 1, fruitId: 1, isActive: 1, 
                result_types: { $filter: {
                                   input: "$types",
                                      as: "type",
                                    cond: { $eq: [ "$$type.isActive", true ] }
                                 } 
                             } } 
   }
])

The Output:

Note the "result_types" empty array where the types.isActive values are false for all elements of "types" array. Only the elements with a value of true are in the result output.

{
        "_id" : "abcdefg",
        "fruitId" : "kipld",
        "isActive" : true,
        "result_types" : [ ]
}
{
        "_id" : "uvwxyz",
        "fruitId" : "kipld",
        "isActive" : true,
        "result_types" : [
                {
                        "name" : "Shimla Apple",
                        "price" : 70,
                        "isActive" : true
                }
        ]
}

Thanks, prasad I implemented it in the same way – Rajath Oct 14 '19 at 10:30 — Rajath, Oct 14 '19 at 10:30

How to return Objects with empty sub Array document if sub Array documents don't satisfy the match condition?

1 Answers1