[{"_id":ObjectId("5146bb52d8524270060001f3"),"post_text":"This is a sample post","user_name":"mark","post_privacy":"public","post_likes_count":0},{"_id":ObjectId("5146bb52d8524270060001f4"),"post_text":"This is a sample post","user_name":"pramod","post_privacy":"public","post_likes_count":0}]

db.collection.find({user_name:"mark"})