db={"user":[{_id:1,username:"joyjeba2",mobile_number:9840347197,profile_url:"http://localhost:3001/user/1599214209351_dp1.jpg",saved_products:[1,2]}],"business":[{_id:1,name:"businessname1",location:"location",contact_number:123456,Products:[{"name":"product","tags":["shoes","slippers"],"description":"its a simple description","lower_price":20,"higher_price":30,"min_order":20,"units":"count","media_urls":["http://localhost:3001/product/1586703106075_DP1.jpg"],"_id":1},{"name":"product","tags":["shoes","slippers"],"description":"its a simple description","lower_price":20,"higher_price":30,"min_order":20,"units":"count","media_urls":["http://localhost:3001/product/1586703106075_DP1.jpg"],"_id":2},{"name":"product","tags":["shoes","slippers"],"description":"its a simple description","lower_price":20,"higher_price":30,"min_order":20,"units":"count","media_urls":["http://localhost:3001/product/1586703106075_DP1.jpg"],"_id":3}]}]}

db.user.aggregate([{$lookup:{from:"business",let:{saved_products:"$saved_products"},pipeline:[{$unwind:"$Products"},{$match:{$expr:{$in:["$Products._id","$$saved_products"]}}},{$replaceRoot:{newRoot:{$mergeObjects:["$Products",{_business_id:"$_id",business_name:"$name",location:"$location"}]}}}],as:"saved_products"}}])