How to export across collection?

Question

I would like to export information across collection. For example, I have 2 collection User and Orders. User contains login info(username) and orders contains the orderID. So when a customer purchases something, the orderID will be generated in the Orders collection and their userID(not the same as username) will be recorded in the order. So I have to reference the userID to find the username within User collection.

I would like to export the orderID alongside the username. Is that possible? As it currently stands, mongodb compass has the export button only when you've selected the collection.

Answer 1

for example your user collection is like this users collection

[{
_id:123,
username:example,
}]

orders collection

[{
_id:234
userId : ObjectId('123')
orderPrice : 300
}]

so you could get order in user object like this with $lookup

db.orders.aggregate([
{
        '$lookup': {
            'from': 'users', // users collection 
            'localField': 'userId', 
            'foreignField': '_id', 
            'as': 'order'
        }
])