Mongoose populate creating sub document directly

Question

I have two mongoose schemas,

Schema A:

{
    field1 : { type : [String] }

}

Schema B:

{
    field2 : { type : ObjectId, ref : 'A' }
}

I want to populate mongoose in such a way that i get the following result :

{
    field2 : field1 of a documnet from A 
}

or

{
    field2 : document of A,
    field1 : field1 field of document A
}

Example:

Document in A { _id : 1 field1 : ["1","2","3"] }

Document in B

{
    _id : 2
    field2 : 1
}

After i populate i want the result to be

{
    _id : 2
    field2 : ["1","2","3"]
}

or

{
    _id : 2
    field2 : {_id : 1 , field1 : ["1","2","3"]}
    field1 : ["1","2","3"]
}

Any one of the two will be appreciated.

Answer 1

This can be achieved using vitual fields in mongoose.

first populate('field2') then create a virtual field field1 and set that equal to field2.field1