mongodb 自增長

mongodb實現mysql AUTO_INCREMENT功能

參照官方文檔（findAndModify實現）：

1.Insert into the counters collection, the initial value for the userid:

   

db.counters.insert(   {      _id: "userid",      seq: 0   })

2.Create a getNextSequence function that accepts a name ofthe sequence. The function uses thefindAndModify() method to atomicallyincrement the seq value and return this new value:

function getNextSequence(name) {   var ret = db.counters.findAndModify(          {            query: { _id: name },            update: { $inc: { seq: 1 } },            new: true          }   );   return ret.seq;}

3.Use this getNextSequence() function during insert().

db.users.insert(   {     _id: getNextSequence("userid"),     name: "Sarah C."   })db.users.insert(   {     _id: getNextSequence("userid"),     name: "Bob D."   })

4.You can verify the results with find():

db.users.find()

文章出處：https://docs.mongodb.com/v3.0/tutorial/create-an-auto-incrementing-field/