db={"books_data":[{_id:ObjectId("61c0a1a895a761d0fe1a1408"),storeName:"Rose Book Store",ownerName:"Rose Ahmed",books:[{name:"economics",totalStock:12,stockStatus:true,_id:ObjectId("61c20d9fcfef88e51e37bdaa")}],createdAt:ISODate("2021-12-21T17:02:30.221Z"),__v:0},{_id:ObjectId("61c17c1481adc44ea10c6083"),storeName:"Toufik Book Store",ownerName:"Toufik Ahmed",books:[{name:"Database",totalStock:14,stockStatus:true,_id:ObjectId("61c217b72e2dc3395071bb26")},{name:"Database",totalStock:14,stockStatus:true,_id:ObjectId("61c217e92e2dc3395071bb2b")},{name:"MySql",totalStock:0,stockStatus:false,_id:ObjectId("61c218142e2dc3395071bb31")}],createdAt:ISODate("2021-12-21T18:03:13.296Z"),__v:0}]}

db.books_data.aggregate([{"$group":{"_id":"null","books":{"$addToSet":"$books"}}},{"$project":{_id:0}}])