Mongoose: Recursive embedded-document in Coffeescr

问题:

Based on this example (which works):

var Comment = new Schema();

Comment.add({
    title : { type: String, index: true }
  , date : Date
  , body : String
  , comments : [Comment]
});

I wanted to create a CoffeeScript version

mongoose = require 'mongoose'
Schema = mongoose.Schema

Person = new Schema
Person.add
  mother: Person
  father: Person

However it returns an error and I don't understand why

TypeError: undefined is not a function
    at CALL_NON_FUNCTION_AS_CONSTRUCTOR (native)
    at Function.interpretAsType (/path/node_modules/mongoose/lib/schema.js:202:10)
    at Schema.path (/path/node_modules/mongoose/lib/schema.js:162:29)
    at Schema.add (/path/node_modules/mongoose/lib/schema.js:110:12)
    at Object.<anonymous> (/path/Models/test.coffee:6:10)
    at Object.<anonymous> (/path/Models/test.coffee:10:4)
    at Module._compile (module.js:411:26)
    at Object.run (/usr/local/lib/node_modules/coffee-script/lib/coffee-script.js:57:25)
    at /usr/local/lib/node_modules/coffee-script/lib/command.js:147:29
    at /usr/local/lib/node_modules/coffee-script/lib/command.js:115:26

EDIT: Okay, I found out that it doesn't work when Person isn't an array (in brackets), but why?

回答1:

Embedded documents can only exist as items in an array. That is by design, you can ask the authors for their reasons :)

You might want to use a DBRef:

Person = new Schema
  mother: { type: Schema.ObjectId, ref: 'Person' }
  father: { type: Schema.ObjectId, ref: 'Person' }

(notice you don't need the add call)

See the docs for populate/DBRef.