[mongodb, 몽고디비 쿼리] Mongodb query on substring of a field

[Question]

I'd like to retrieve results equals to departement codes, but I'm storing postal codes. Something like that...

db.collection.find({
    {$substr:[cp,0,2]}:{$eq:dpt}
});

[Answer]

You can use aggregation $project to create department code column. Then find by $match your condition

    db.collection.aggregate(
            [ 
                { $project:{
                    "cp" : 1,
                    department_code: { $substr: ["$cp", 0, 2]}
                    }
                }
                ,{ $match : { department_code: 'department code to find' } }
            ]
        );

[출처] https://stackoverflow.com/questions/51591901/mongodb-query-on-substring-of-a-field

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