Node和Mongoose创建/使用字段为每个新添加的字段增加+1

Question

I'm going to try and keep this as simple as possible. I've spent all day testing modules to do this, and at this point have gotten so confused with everything I figured this would be my best option.

I have a Schema:

var AppSchema = new mongoose.Schema({
    appid: { type: Number },
    appname: { type: String },
    appdesc: { type: String }
});
app.db.model('userApp', AppSchema);

Using Express and processing a POST, I then want to create "a new app"

app.post('/app/new', function (req, res) {
    var newApp = app.db.models.userApp({
        appid: functionToIncreaseByOne(),
        appname: req.param('appname'),
        appdesc: req.param('appdesc')
    });
    newApp.save();
});

I removed most of the bloat in there, redirects, etc, just to keep this simple. So what I would like to do is to have the APPID be set at 1 first the first app added, and then increase +1 for each new app that is added. It seems so simple but i've gone through so many complex examples my head just hurts now.

I thought about just using .find and then orderby to find the app with the highest appid, then just use that and add +1 to it, but i'm sure there has to be another, easier way. I DON'T want the appid to change when there is an update, the only time I want it to be set is on that first POST route to create the new app.

If someone could please help me out here or at least point me in the right direction, I would greatly appreciate it.

Answer 1

I can see several ways to do so.

First , you may store last_id in a global variable:

var last_id = 0;

app.post('/app/new', function (req, res) {
  var newApp = app.db.models.userApp({
    appid: ++last_id,
    appname: req.param('appname'),
    appdesc: req.param('appdesc')
  });
  newApp.save();
});

You may add a proper initialization of last_id , so it'll "catch up" with your database when your application starts.

The only disadvantage of this approach is that you can't use it if you have several node.js processes.

Second , you may query your database each time you want to create new document:

app.post('/app/new', function (req, res, next) {
  app.db.models.userApp.find()
    .sort({_id: -1})
    .limit(1)
    .select('_id')
    .exec(function (err, docs) {
      if (err) return next(err);
      var newApp = app.db.models.userApp({
        appid: docs[0]._id,
        appname: req.param('appname'),
        appdesc: req.param('appdesc')
      });
      newApp.save();
    })
});

But there is no way to guarantee that the next find operation will occur after the previous save operation. So, there is a chance that your app will try two save two different docs with one _id . It's why you should avoid this solution if possible.

Third , you may use some other storage (eg Redis) to atomically increment last_id every time you're reading it:

var RedisClient = require('redis').createClient()

app.post('/app/new', function (req, res, next) {
  RedisClient.incr('last_id', function (err, next_id) {
    if (err) return next(err);
    var newApp = app.db.models.userApp({
      appid: next_id,
      appname: req.param('appname'),
      appdesc: req.param('appdesc')
    });
    newApp.save();
  })
});

This solution is the best one, but it require additional database to be installed.