Database
db={"books":[{_id:1,ISBN10:"081",ISBN13:"978",Title:"The Deal",Cover:"www.openisbn.com/cover/",Publisher:"Forge",Pages:"320",Authors_arr:["Joe Hutsko"]}],"book_copies":[{_id:2,book_id:"081",branch_id:1,no_of_copies:1},{_id:3,book_id:"081",branch_id:2,no_of_copies:1}]}
Query
db.books.aggregate([{$lookup:{from:"book_copies",localField:"ISBN10",foreignField:"book_id",as:"book_copies",pipeline:[{$project:{_id:0,book_id:0}}]}}])