为什么我不能在 mongoose / mongodb 中增加？

Question

Im trying to increment but the result always shows that it is undefined.

var mongoose = require('mongoose');

var TestSchema = mongoose.Schema({

    total: Number


});

var Test = mongoose.model('Test', TestSchema);

var arr = [2,4,5,6,7,8];
var test = new Test();

arr.forEach(function(item) {
    console.log(item);
    test.total += item;
});

console.log(test.total);

console.log(test.total) will printout undefined.

Answer 1

It doesn't work because "total" is not defined to start with. So instead define something:

var mongoose = require('mongoose'),
    Schema = mongoose.Schema;

var testSchema = new Schema({
  total: Number
});

var Test = mongoose.model( 'Test', testSchema );

var arr = [2,4,5,6,7,8];

var test = new Test({ "total": 0 });

arr.forEach(function(item) {
  console.log(item);
  test.total += item;
});

console.log(test);

Outputs:

2
4
5
6
7
8
{ _id: 5641850e7a8c9b001842c6d2, total: 32 }

Just like it should.

Alternately, at least supply a schema default.

var testSchema = new Schema({
  total: { type: Number, default: 0 }
});

But if nothing is there, then the value is undefined and trying to increment an undefined value just returns nothing in result.