mongoose的population数据填充关联不成功
跟着项目做数据关联不成功，然后我找了网上的demo也是不成功，很无语。
demo如下，首先创建三个model :User、Post、Comment，然后将数据插入到数据库保存，在访问服务器时候执行createServer里面的代码，populate('posts', 'title')将Post集合的title字段填充关联到User集合里的posts字段。但是打印效果是：
[ { name: 'aikin', _id: 595639aa9a73292826000001, posts: [] } ]
[ { name: 'aikin', _id: 595639aa9a73292826000001, posts: [] } ]为什么posts字段为空呢？
完整代码如下：
const http = require('http');
const mongoose = require('mongoose');
var Schema = mongoose.Schema;
var ObjectId = Schema.Types.ObjectId;
var UserSchema = new Schema({
name : { type: String, unique: true },
posts : [{ type: ObjectId, ref: 'Post' }]
});
var User = mongoose.model('User', UserSchema);
var PostSchema = new Schema({
poster : { type: ObjectId, ref: 'User' },
comments : [{ type: ObjectId, ref: 'Comment' }],
title : String,
content : String
});
var Post = mongoose.model('Post', PostSchema);
var CommentSchema = new Schema({
post : { type: ObjectId, ref: "Post" },
commenter : { type: ObjectId, ref: 'User' },
content : String
});
var Comment = mongoose.model('Comment', CommentSchema);
var db = mongoose.connect('mongodb://localhost/alan');
db.connection.on("error", (error) => {
console.log("数据库连接失败：" + error);
});
db.connection.on("open", () => {
console.log("——数据库连接成功！——");
// createData(); // 插入数据
});
function createData() {
var users ;
var posts ;
var comments ;
users = {
name : 'aikin',
// posts : [new ObjectId]
};
posts = {
title : 'post-by-luajin',
// poster : new ObjectId,
// comments : [new ObjectId]
};
comments = {
content : 'comment-by-aikin',
// commenter : new ObjectId,
// post : new ObjectId
};
var _user = new User(users);
var _post = new Post(posts);
var _comment = new Comment(comments);
_user.save((err, user) => {
if (err) console.log(err);
console.log(user);
});
_post.save((err, post) => {
if (err) console.log(err);
console.log(post);
});
_comment.save((err, comment) => {
if (err) console.log(err);
console.log(comment);
});
}
http.createServer((req, res) => {
res.writeHead(200,{"Content-Type": "text/plain"});
/*CN.findOne({name: 'Alan'}, (err, data) => {
console.log(data);
});*/
User.find()
.populate('posts', 'title')
.exec(function(err, docs) {
console.log(docs); // post-by-aikin
res.write("hello");
res.end();
});
}).listen(4000,() => {
console.log("Server run at port", 4000);
});补充一下，由于我的系统是win7 32位但目前的mongodb都不支持32位的，所以我装了个2012年的mongodb 2.0.4版本，和同时间段的mongoose 2.6.0版本
