Mongoose Guide-Population

MongoDB does not join, but sometimes we need to refer to other collection documents, this time we need to populate.

We can populate a single document, multiple document, plain object, multiple plain objects, or all object returned by query.

var mongoose = require (' Mongoose '); var Schema = Mongoose. Schema;var Personschema = new Schema ({    _id:number,     name:string,     age:number,     stories: [{type: Schema.Types.ObjectId, ref: ' Story '}]}), var storyschema = new Schema ({     _creator: {type:number, ref: ' Person '},     Title:string,     fans: [{type:number, ref: ' Person '}]}); var story = Mongoose.model ("story", Storyschema); var person = m Ongoose.model (' person ', personschema);

So far we've created two of the model. The person model has a stories field that is a collection of Objectid. Ref is telling Mongoose which model should be popluate.

Story has a _creator field that is number type. He's the ID of Personschema.

Saving ref

Save a ref

var arron = new Person ({_id:0, Name: ' Aaron ', age:100}), Arron.save (function (err) {   if (err) return HandleError (ERR); C1/>var story1 = new Story ({      titile: ' Once upon a Timex ',      _creator:arron._id    //Assigned person's _id   });      Story1.save (function (err) {      if (err) return HandleError (ERR);    });});

Populate

The _creator that fills the story

Story  . FindOne ({title: ' Once upon a Timex ')  . Populate (' _creator ')  . EXEC (Fucntion (err, story) {      if (err) return HandleError (err);      Console.log (Story._creator.name)//Aaron   });

Field selection

If we don't want to fill the story with the whole _creator, we just want to populate _creator's name.

Story.findone ({title:/timex/i}). Populate (' _creator ', ' name ')//Only return the Persons name.exec (function (err, story) {  if (err) return HandleError (err);    Console.log (' The creator is%s ', story._creator.name);  Prints "The creator is Aaron"    console.log (' The Creators age is%s ', story._creator.age);  Prints "The creators is Null"})

Fill multiple paths at once

If we want to fill more than one path at a time, what's wrong?

Story.find (...). Populate (' Fans author ')//Space delimited path names.exec ()

Another way of writing

Story.find (...). Populate (' fans '). Populate (' author '). EXEC ()

Fill by condition

Story.find (...). Populate ({  path: ' Fans ',  match: {age: {$gte: +}},  select: ' Name-_id ',  options: {Limit:5}}). EXEC ()

　　

Mongoose Guide-Population