CODEWITHSUNDEEP
pythonmongodbmongodb-querypymongo
daman behl
daman behl

Reputation: 63

$toString alternative to convert '_id' from type ObjectId() to string in mongoDB version 3.6.3?

I am performing an aggregation which is performing joins using $lookup to join 3 collections based on a $match condition which involves matching a list of '_id' values which I already have available as a list in python to that of ObjectId("") version that is present in mongoDb. In version 4.0 $toString is the way to go but i cannot find a suitable alternative for this

criteria = [
        {
            '$project': {
                '_id': {
                    '$toString': '$_id'
                }
            }
        },
        {
            '$lookup': {
                'from': 'clients',       # other table name
                'localField': 'clientId',   # name of users table field
                'foreignField': '_id',  # name of userinfo table field
                'as': 'client_info'  # alias for userinfo table
            }
        },
        # $unwind used for getting data in object or for one record only
        {'$unwind': '$client_info'},
        # Join with job_info table
        {
            '$lookup': {
                'from': 'jobs',
                'localField': 'jobId',
                'foreignField': '_id',
                'as': 'job_info'
            }
        },
        {'$unwind': "$job_info"},
        # conditions willl go here
        {
            '$match': {
                '$and': [{'_id': {'$in': pipline_array}}]
            }
        },
        {
            '$project': {
                '_id': 1,
                'client_name': "$client_info.name",
                'job_name': "$user_role.name",
            }
        }
    ]

Upvotes: 2

Views: 1129

Answers (1)

whoami - fakeFaceTrueSoul
whoami - fakeFaceTrueSoul

Reputation: 17915

If you wanted your aggregation query to convert string to ObjectId() or vice-versa on the fly by itself then you need to use MongoDB version >= 4.0 - where you'll have operators $toObjectId() & $toString() to do the conversion. But if your MongoDB version is < 4.0 then you'll have no option other than to convert & update your field in all documents of one collection to match with type of field in other collection.

But your issue is different, as you're passing in a list of strings & comparing it against _id using $in, So instead you can convert string to ObjectId() & pass-in as input like below :

from bson.objectid import ObjectId


pipline_array = ['5d76b2c847c8d3000184a090', '5d7abb7a97a90b0001326010']
pipline_array_converted = []


for i in pipline_array:
    pipline_array_converted.append(ObjectId(i))

Upvotes: 2

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