Project field in embedded document within embedded array

Question

I have the following query:

 cursor=self.postCol.aggregate([
      { \"$graphLookup\" : {
        \"from\": \"pCol\",
        \"startWith\": \"$parent\",
                


        

Answer 1

You can replace the else condition with below using $let operator.

 {
    $let: {
        vars: {
            obj: {
                "$arrayElemAt": ["$parents", 0]
            }
        },
        in: "$$obj.pValue"
    }
 }