NodeJS - Mongoose (Object has no method "id")

When I try this code in my Application:

app/models/Post.coffee

mongoose      = require "mongoose"
CommentModel  = require "./Comment"
Comment       = CommentModel.Schema
Schema        = mongoose.Schema

Post = new Schema {
    title: String,
    slug: {type: String, index: { unique: true, dropDubs: true }},
    content: String,
    author: String,
    tags: [String],
    comments: [Comment],
    created: { type: Date, default: Date.now }
}

Post.statics.findBySlug = (slug, cb) ->
    this.model("Post").findOne({ slug: slug }, cb)

PostModel = mongoose.model "Post", Post

module.exports = PostModel

app/models/Comment.coffee

mongoose  = require("mongoose")
Schema    = mongoose.Schema

Comment = new Schema {
    author: String,
    content: String,
    approved: Boolean,
    created: { type: Date, default: Date.now }
}


CommentModel = mongoose.model "Comment", Comment

module.exports = CommentModel

app/controllers/PostsController.coffee (Just one method)

commentDestroy: (req, res, next) ->
    Post.findBySlug req.params.slug, (err, doc) ->
        if (err)
            return next err

        if doc == null
            res.send 404
            return

        doc.comments.id(req.params.comment).remove()
        doc.save (err) ->
            if err
                next err

            res.json doc

It ends with error:

TypeError: Object [object Object],[object Object],[object Object],[object Object],[object Object] has no method 'id'
    at Promise.PostsController.commentDestroy (/home/r41ngoloss/Projects/www/my-express/app/controllers/PostsController.js:88:22)
    at Promise.addBack (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/promise.js:128:8)
    at Promise.EventEmitter.emit (events.js:96:17)
    at Promise.emit (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/promise.js:66:38)
    at Promise.complete (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/promise.js:77:20)
    at Query.findOne (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/query.js:1533:15)
    at model.Document.init (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/document.js:229:11)
    at model.init (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/model.js:192:36)
    at Query.findOne (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/query.js:1531:12)
    at exports.tick (/home/r41ngoloss/Projects/www/my-express/node_modules/mongoose/lib/utils.js:408:16)

I already tried to find solution for my problem, but i found just this and I think, that I have schemas in right order (By require).

Thanks for every answer.