show collections
db.topics.find()
db.users.find()
db.topics.find()
db.user.find()
db.users.find()
show collections
db.replys.find()
show collections
show collections
db.topics.find()
db.users.find()
db.topics.find()
db.replys.find()
db.topics.find()
show collections
db.categories.find()
show collections
db.topics.find()