db={"Employees":[{"_id":ObjectId("5e5eb6222c6306fe68ae713f"),"Empid":1.0,"Name":"John","Age":41.0,"Location":"Belfast","deptid":"D101"},{"_id":ObjectId("5e5eb68f4dc32ed4642a3327"),"Empid":1.0,"Name":"Jess","Age":11.0,"Location":"Belfast","deptid":"D102"}],"Dept":[{"_id":ObjectId("5e5eb64d2c6306fe68ae7140"),"deptID":"D101","deptNM":"HR","deptPr":"O"},{"_id":ObjectId("5e5eb7b74dc32ed4642a52a2"),"deptID":"D102","deptNM":"HR-2","deptPr":"H"},{"_id":ObjectId("5e5eb7cf4dc32ed4642a54e3"),"deptID":"D103","deptNM":"Dev","deptPr":"D"}]}

db.Employees.aggregate([{$match:{Age:{$gt:40}}},{$lookup:{from:"Dept",localField:"deptid",foreignField:"deptID",as:"HR_EMP"}},{$unwind:"$HR_EMP"},{$match:{"HR_EMP.deptNM":"HR"}},{$project:{Empid:1,Name:1,Location:1,deptNM:"$HR_EMP.deptNM",deptPr:"$HR_EMP.deptPr"}}])