MongoDB没有join, 但是有的时候我们需要引用其它collection的documents, 这个时候就需要populate了.
我们可以populate单个document, 多个document, plain object, multiple plain objects或query返回的全部object.
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 = mongoose.model('Person', personSchema);
目前为止我们创建了两个model. Person model有一个stories字段是以个ObjectId的集合. ref是告诉mongoose哪个model应该被popluate.
Story有一个_creator字段是Number类型的他是personSchema的Id
Saving ref
保存一个ref
var arron = new Person({_id:0, name: 'Aaron', age: 100});
arron.save(function(err){
if(err) return handleError(err);
var story1 = new Story({
titile: 'Once upon a timex',
_creator: arron._id //分配person的_id
});
story1.save(function(err){
if(err) return handleError(err);
});
});
Populate
填充story的_creator
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
如果我们不想为story填充整个_creator 我们只想填充_creator的name怎么搞呢？
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 age is null'
})
一次填充多个paths
如果我们想一次填充多个path怎么过搞呢
Story
.find(...)
.populate('fans author') // space delimited path names
.exec()
另一种写法
Story
.find(...)
.populate('fans')
.populate('author')
.exec()
按条件填充
Story
.find(...)
.populate({
path: 'fans',
match: { age: { $gte: 21 }},
select: 'name -_id',
options: { limit: 5 }
})
.exec()