Finding the highest value of object's field with specified _id in array of objects in mongodb

Question

I am new to mongodb. I am doing simple application that uses this database. Here is my doctors collection structure:

{
    _id: 1,
    name: "David",
    specialisation: "dentist",
    description: "Super dentist",
    treatments: [
        {
            _id: 0,
            price: 2200
        },
        {
            _id: 2,
            price: 200
        },
        {
            _id: 5,
            price: 2500
        },
        {
            _id: 8,
            price: 3200
        },
        {
            _id: 13,
            price: 2050
        }
    ],
    hospitals: [1, 2, 8, 5, 20]
},
{
    _id: 2,
    name: "John",
    specialisation: "dentist",
    description: "Super dentist",
    treatments: [
        {
            _id: 2,
            price: 2500
        }
    ],
    hospitals: [1]
}

What I want to do, is to get the max value of a treatment with specified id of all doctors in collection. For example in this case if I want to check treatment with _id = 2 it should return 2500, as it is written in John's object.

Any help would be appreciated. Thanks.

In this structure u have to traverse treatments array then do find _id:2 , then keep max price field,then same process for next object and compare max price , this kinda approach vl work but however this seems inefficient structure, how about this treatments:{1:"2200",2:"200",5:"2500",8:"3200",13:"2050"} then u vl be able to do like treatments[2] or treatments:{1:{key1:val1,key2:val2},2:{key1:val1,key2:val2}} tell which approach suits you , vl help u out in that approach's code — Aishwat Singh
– Aishwat Singh, Commented Nov 7, 2015 at 17:44
Unfortunatelly I have to keep this structure. I'm not sure what u mean by 'vl'. — kuba12
– kuba12, Commented Nov 7, 2015 at 17:54
ahh, ok. I've googled it so far and didn't found any interesting info :D — kuba12
– kuba12, Commented Nov 7, 2015 at 17:59
one doubt treatment with _id = 2 it should return 2500, as it is written in John's object here _id=2 u mean outside _id(above name:"john") or the one inside array ? — Aishwat Singh
– Aishwat Singh, Commented Nov 7, 2015 at 18:00

Aishwat Singh · Accepted Answer · 2015-11-07 18:23:22Z

1

Named ur collection as stack try this

db.stack.aggregate([ {$project:{"treatments._id":1, "treatments.price":1}}, 
{$unwind:"$treatments"},{$match:{"treatments._id":2}},
{$sort:{"treatments.price":-1}}, {$limit:1} ]);

result: { "_id" : 2, "treatments" : { "_id" : 2, "price" : 2500 } }

ref: https://docs.mongodb.org/manual/reference/operator/aggregation/unwind/

answered Nov 7, 2015 at 18:23

Aishwat Singh

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