自动增加猫鼬模型中的数字字段

Question

I was using MySql DB for my website and now updating it to MongoDB. There were columns in some tables getting auto-incremented and I want to make sure that the same continues. Below are my finding so far but none is working. Using mongoose-auto-increment plugin

var mongoose = require('mongoose'),
    Schema = mongoose.Schema,
    autoIncrement = require('mongoose-auto-increment');

var connection = mongoose.createConnection("mongodb://localhost/myDatabase");

autoIncrement.initialize(connection);

EmborderSchema.plugin(autoIncrement.plugin, {
  model: 'Emborder',
  field: 'emborder_id',
  startAt: 28855,
  increamentBy: 1
});

Using pre save hook:

EmborderSchema.pre('save', function (next) {
  if (this.emborder_id == undefined) {
    Emborder.findOne({})
      .sort({emborder_id: -1})
      .exec(function (err, data) {
        this.emborder_id = data.emborder_id + 1;
        next();
      })
  } else {
    next();
  }
});

Using the first method gives me an error

E11000 duplicate key error collection: 24hd.24hd_emborder index: emborder_id_1 dup key: { 23345 }

Second method gives this error

E11000 duplicate key error collection: 24hd.24hd_emborder index: emborder_id_1 dup key: { : null }

Note: emborder_id was the primary key in my old Mysql DB and in this code value of emborder_id is undefined as I am adding a new record.

Please help me finding whats going wrong in this approch.

Answer 1

I will recommend second approach for you.

EmborderSchema.pre('save', function (next) {
  var self = this;
  if (self.emborder_id == undefined) {
    Emborder.findOne({})
      .sort({emborder_id: -1})
      .exec(function (err, data) {
        if(!data.emborder_id){
         self.emborder_id = 1;
         next();
        }else{
          self.emborder_id = data.emborder_id + 1;
          next();
        }
      })
    next();
  }
});

For more you can read about Context in javascript.

For example , inside of a function, when you say: “this.accoutNumber”, you are referring to the property “accoutNumber”, that belongs to the object within which the function is executing.

If the object “foo” has a method called “bar”, when the JavaScript keyword “this” is used inside of “bar”, it refers to “foo”. If the function “bar” were executed in the global scope, then “this” refers to the window object.

Context example taken from --> https://blog.kevinchisholm.com/javascript/difference-between-scope-and-context/