CODEWITHSUNDEEP
mongodbmongodb-queryaggregation-frameworkpymongopymongo-3.x
Induraj PR
Induraj PR

Reputation: 304

Performing Repeated filtering in mongodb

I want to get the names of people who work in bmw and use these names as filter to find and return the documnents containing the field "car". So the end result must be the last two documents given in this example.

[
    {"_id": "235", "name": "indu", "dob": "31/4/15", "company": "bmw"},
    {"_id": "236", "name": "prith", "dob": "01/4/98", "company": "bmw"},
    {"_id": "237", "name": "rames", "dob": "07/4/00", "company": "renault"},
    {"_id": "238", "name": "indu", "salary": "10,000", "car": "yes", "married": "yes"},
    {"_id": "239", "name": "prith", "salary": "80,000", "car": "yes", "children": "no"}
]

I appreciate your help, Thanks in advance

Upvotes: 1

Views: 82

Answers (1)

Tom Slabbaert
Tom Slabbaert

Reputation: 22296

You want to use $exists

names = db.collection.distinct{"name", {"company": "bmw"})
db.collection.find({"car": {"$exists": true}, "name": {"$in": names}})

You can also do it in 1 aggregation call although I would not recommend it as It's less efficient.

db.collection.aggregate([
    {
       "$match": {
           "company": "bmw"
       }   
    },
    {
        $lookup: {
            from: "this_collection",
            localField: "name",
            foreignField: "name",
            as: "roots"
        }
    },
    {
        "$unwind": "$roots"
    },
    {
        "$replaceRoot": {
            "newRoot": "$roots"
        }
    },
    {
        "$match": {
            "car": {"$exists": true}
        }
    }
])

Upvotes: 1

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