如何通过$ inc在猫鼬中增加价值

Question

I am trying to increment a field value using $inc without too much success. I have the following schema:

var postSchema = mongoose.Schema({
  title         : { type: String, required: true },
  body          : { type: String, default: '' },
  counter       : counterSchema
});

var counterSchema = mongoose.Schema({
  upvotes       : { type: Number, default: 0, min: 0 },
  downvotes     : { type: Number, default: 0, min: 0 },
  view          : { type: Number, default: 0, min: 0 }
});

I am trying to increment values in counter , and what I have is:

  ...
  let where = `{ '_id': ObjectId("${req.body.pid}") }`: 
  let update = req.body.action === 'up' ? "{ '$inc': { 'counter.upvotes': 1 } }"
                                        : "{ '$inc': { 'counter.downvotes': 1 } }";

  Post.findOneAndUpdate(where, update, {'new': true}, (err, post) => {
    if (err) return next(err);
    console.log('post=' + JSON.stringify(post));
  ...

I was able to successfully increment in mongod using the statement,

db.posts.update({_id: ObjectId('56cd78fddfe1372131a04b4d')}, {$inc: {'counter.upvotes': 1}})

so I initially thought it had to do with Mongoose syntax, and tried number of variations including:

1. Using collection...update().exec(... ) format
2. Enclosing keys and values in single, double, no quote
3. Omitting ObjectId , ie, { '_id': id) }

But so far no luck. Any help would be greatly appreciated.

PS. The code does execute successfully without error, and I get back a post since I set the option to {'new': true} . It's just that either of post.counter.[upvote | downvote] is incremented in what's returned nor in the mongodb.

Answer 1

Your where and update variables need to contain objects, not strings.

So it should be like this instead:

let where = { '_id': ObjectId(req.body.pid) };
let update = req.body.action === 'up' ? { '$inc': { 'counter.upvotes': 1 } }
                                      : { '$inc': { 'counter.downvotes': 1 } };