Database
db={"exams":[{"_id":{"$oid":"639300717660dc72b8827bcb"},"studentId":"6392ffa38ce065c410977f66","questions":[{"status":"correct","question":{"$oid":"633fdf2f6da53819401b4807"},"selectedAnswer":{"$oid":"633fcbd443c1a872f866e683"}},{"status":"incorrect","question":{"$oid":"633fdf316da53819401b52a8"},"selectedAnswer":{"$oid":"633fcbd443c1a872f866e670"}},{"status":"incorrect","question":{"$oid":"633fdf2e6da53819401b4590"},"selectedAnswer":{"$oid":"633fcbd443c1a872f866e661"}},]}],"questions":[{"_id":{"$oid":"633fdf2e6da53819401b4590"},"options":[{"_id":"633fcbd443c1a872f866e660","optionValue":"This a first option","isCorrect":true,"stat":"0.00"},{"_id":"633fcbd443c1a872f866e661","optionValue":"This is second Option","isCorrect":false,"stat":"00.00"},{"_id":"633fcbd443c1a872f866e662","optionValue":"This Is third Option","isCorrect":false,"stat":"0.00"},{"_id":"633fcbd443c1a872f866e663","optionValue":"This is fourth Option","isCorrect":false,"stat":"0.00"}],"status":true,"questionValue":"This is a sample question for demonstration",},{"_id":{"$oid":"633fdf316da53819401b52a8"},"options":[{"_id":"633fcbd443c1a872f866e670","optionValue":"This a first option","isCorrect":true,"stat":"0.00"},{"_id":"633fcbd443c1a872f866e671","optionValue":"This is second Option","isCorrect":false,"stat":"00.00"},{"_id":"633fcbd443c1a872f866e672","optionValue":"This Is third Option","isCorrect":false,"stat":"0.00"},{"_id":"633fcbd443c1a872f866e673","optionValue":"This is fourth Option","isCorrect":false,"stat":"0.00"}],"status":true,"questionValue":"This is a sample question for demonstration",},{"_id":{"$oid":"633fdf2f6da53819401b4807"},"options":[{"_id":"633fcbd443c1a872f866e680","optionValue":"This a first option","isCorrect":true,"stat":"0.00"},{"_id":"633fcbd443c1a872f866e681","optionValue":"This is second Option","isCorrect":false,"stat":"00.00"},{"_id":"633fcbd443c1a872f866e682","optionValue":"This Is third Option","isCorrect":false,"stat":"0.00"},{"_id":"633fcbd443c1a872f866e683","optionValue":"This is fourth Option","isCorrect":false,"stat":"0.00"}],"status":true,"questionValue":"This is a sample question for demonstration",}]}
Query
db.exams.aggregate([{$lookup:{from:"questions",localField:"questions.question",foreignField:"_id",as:"questions"}},])