Database

db={"userCollections":[{_id:ObjectId("6236ba6b465ff537abfaa64c"),firstName:"user",lastName:"uer",password:"$2a$10$2SX2R1lFEErvcJnO1oGafOK/BRnQ.PG7oLHX0LJ/uuEhrk81NcbnO",email:"user1@gmail.com",phone:5465465645,premiumUser:false,status:true,authorStatus:false,indroduction:"dfghjk",city:"asdfadf",state:"asdfasdf",address:"sdfghjksdaf",wishlistItems:[ObjectId("6231db05a8b12caba4feb39a"),ObjectId("6233118f2f06967703e70a4b"),ObjectId("6231daa03eedc2006c23b98d"),ObjectId("6231d3f1b7b4d0299b8b5e2f"),ObjectId("6230dbf77f64b9b25f3939c0"),ObjectId("6230d44f6250bcb698a4a5fb")],createdAt:ISODate("2022-03-20T05:23:55.086Z"),updatedAt:ISODate("2022-03-20T05:25:20.516Z"),__v:0}],"postCollections":[{_id:ObjectId("62330fb82f06967703e70a48"),postTitle:"GET A PEEK INTO THE FORGOTTEN SIDE OF ASAKUSA,TOKYO",subTitle:"Are you a first time visitor to Japan and looking ..",postIndroduction:"Are you a first time visitor to Japan and ..",postContent:"Pearl Harbor Attack had awakened a sleeping gia.",place:"JAPAN",date:ISODate("2016-05-12T00:00:00.000+00:00"),authorId:ObjectId("622ad301141ddb7050a78634"),likeCount:0,image1:"https://res.cloudinary.com/ashproduct/image/upload/v1647513503/pzhaddu...",image2:"https://res.cloudinary.com/ashproduct/image/upload/v1647513506/guooaum...",image3:"https://res.cloudinary.com/ashproduct/image/upload/v1647513514/rbyh2p4...",image4:"https://res.cloudinary.com/ashproduct/image/upload/v1647513519/vwwqerz...",image5:"https://res.cloudinary.com/ashproduct/image/upload/v1647513527/xqyukzj...",/** ....*/},{_id:ObjectId("6231d3f1b7b4d0299b8b5e2f"),postTitle:"GET THE BEST SUSHI IN ASAKUSA,TOKYO",subTitle:"Are you a first time visitor to Japan and looking ..",postIndroduction:"Are you a first time visitor to Japan and ..",postContent:"Sushi is awesome ...",place:"JAPAN",date:ISODate("2016-05-19T00:00:00.000+00:00"),authorId:ObjectId("622ad301141ddb7050a78634"),likeCount:0,image1:".../sushi1.png",image2:".../sushi2.png",image3:".../sushi3.png",/** ....*/}]}

Query

db.userCollections.aggregate([{"$match":{"_id":ObjectId("6236ba6b465ff537abfaa64c")}},{"$lookup":{"from":"postCollections","localField":"wishlistItems","foreignField":"_id","as":"wishPosts"}}])

Result