callQueue method in mongoose schema constructor - node.js

Question

I have problem to understand the line: this.callQueue = [ [ 'pre', [ 'save', beforeSave ] ] ];
Here is the line where it locates at:
var util = require('util');
var Schema = require('mongoose').Schema;
var counter = require('./counter');
var utils = require('./utils');
/**
* Base Schema constructor.
*
* ####Example:
*
* var user = new BaseSchema({ name: String });
* var post = new BaseSchema({ content: String });
*
* // setting schema options
* new BaseSchema({ name: String }, { _id: false, autoIndex: false })
*
* ####Options:
*
* - [autoIndex](/docs/guide.html#autoIndex): bool - defaults to true
* - [bufferCommands](/docs/guide.html#bufferCommands): bool - defaults to true
* - [capped](/docs/guide.html#capped): bool - defaults to false
* - [collection](/docs/guide.html#collection): string - no default
* - [id](/docs/guide.html#id): bool - defaults to true
* - [_id](/docs/guide.html#_id): bool - defaults to true
* - `minimize`: bool - controls [document#toObject](#document_Document-toObject) behavior when called manually - defaults to true
* - [read](/docs/guide.html#read): string
* - [safe](/docs/guide.html#safe): bool - defaults to true.
* - [shardKey](/docs/guide.html#shardKey): bool - defaults to `null`
* - [strict](/docs/guide.html#strict): bool - defaults to true
* - [toJSON](/docs/guide.html#toJSON) - object - no default
* - [toObject](/docs/guide.html#toObject) - object - no default
* - [versionKey](/docs/guide.html#versionKey): bool - defaults to "__v"
*
*
* #param {Object} definition
* #inherits NodeJS EventEmitter http://nodejs.org/api/events.html#events_class_events_eventemitter
* #event `init`: Emitted after the schema is compiled into a `Model`.
* #api public
*/
function BaseSchema() {
Schema.apply(this, arguments);
this.callQueue = [ [ 'pre', [ 'save', beforeSave ] ] ];
this.add({
_id: Number,
createTime: Number,
modifyTime: Number
});
}
/**
* set default value before save to db
*
*
* #param {Function} next
*/
function beforeSave(next) {
var model = this;
if(model.isNew) {
model.modifyTime = model.createTime = Date.now();
counter.getNextId(model.collection.name + '_id', function(err, id) {
model._id = id;
next();
});
}
else {
model.modifyTime = Date.now();
next();
}
}
util.inherits(BaseSchema, Schema);
module.exports = BaseSchema;
Also I think the usage is like this
var Post = new BaseSchema({
title: String,
tags: Array,
content: String,
creator: String,
avatar: String,
comments: [Comment],
pv: Array,
reprint: { type: Object, default: {} },
lastUpdateTime: String
}, options);
Post.pre('save', function(next) {
if(this.isNew) {
this.lastUpdateTime = utils.formatDate(Date.now());
}
next();
})
Also here is the project github link: [https://github.com/smadey/node-mongoose-blog]. The code is in models file

Answer 1

this.callQueue = [ [ 'pre', [ 'save', beforeSave ] ] ] is internally adding a pre save middleware for all the schemas that are inherited from it. For example is the Post schema will have now two pre save hooks attached to it:
First one is the beforeSave hook attached with BaseSchema
Second one is the hook that is attached with Post schema
Internally all hooks are stored in callQueue array. If you log that variable, you'll see two callbacks for those two hooks:
> console.log(Post.callQueue)
[ [ 'pre', [ 'save', [Function: beforeSave] ] ],
[ 'pre', { '0': 'save', '1': [Function] } ] ]