Mongodb $lookup Not working with _id

Question

wend try with this query, return the lookup is empty

db.getCollection(\'tests\').aggregate([
    {$match: {typet:\'Req\'}},
    {$project: {incharge:1}},
            


        

Answer 1

Your lookup query is perfect, but the problem is you are storing incharge as string into the db, whereas the _id : ObjectId('theID') is an Object and not just string and you cannot compare a string (' ') with an object ({ }). So, the best way is to store the incharge key as an object(mongoose.Schema.ObjectId) and not as string in the schema.