db={"collection1":[{name:"name1",city:"city1"},{name:"name2",city:"city2"}],"collection2":[{name:"name1",education:"college",occupation:"engineer",address:"address1"},{name:"name2",education:"highschool",occupation:"manager",address:"address2"},{name:"name3",education:"highschool",occupation:"manager",address:"address3"}]}

db.collection2.aggregate([{"$lookup":{"from":"collection1","localField":"name","foreignField":"name","as":"join"}},{$addFields:{join:{$ifNull:[{"$arrayElemAt":["$join",0]},[]]}}},{"$addFields":{"city":"$join.city",join:"$$REMOVE",address:"$$REMOVE"}}])