about mongoose populate relation a string field - node.js

Question

I have two Schema
1 - User
UserSchema = new db.Schema({
email: {type: String, required: true},
pass: {type: String, required: true},
nick: {type: String, required: true},
admin: {type: String, default: ''},
reg: {type: Date, default: Date.now}
});
2 - Article
ArticleSchema = new db.Schema({
title: {type: String, required: true},
alise: {type: String},
time: {type: Date, defaults: Date.now},
view: {type: Number, defaults: 0},
author: {type: String},
content: {type: String},
classes: {type: db.Schema.Types.ObjectId, ref: 'Classes'},
user: {type: String, ref: 'User'}
});
I want ArticleSchema user field relation UserSchema nick.
my code:
Model.findOne({}).populate('classes user').exec(function(err, res){
if(err){
cb(err);
}else{
cb(null, res);
}
});
This is not working
message: 'Cast to ObjectId failed for value "tudou" at path "_id"'
What should I do?

Answer 1

Apparently you are using Mongoose, right?
If yes, to do it you must use db.Schema.Types.ObjectId in the ArticleSchema user field. So, your ArticleSchema should looks like this:
ArticleSchema = new db.Schema({
title: {type: String, required: true},
alise: {type: String},
time: {type: Date, defaults: Date.now},
view: {type: Number, defaults: 0},
author: {type: String},
content: {type: String},
classes: {type: db.Schema.Types.ObjectId, ref: 'Classes'},
user: {type: db.Schema.Types.ObjectId, ref: 'User'}
});
According to documentation:
There are no joins in MongoDB but sometimes we still want references to documents in other collections. This is where population comes in.
So, taking a look here, we can do something like that:
//To create one user, one article and set the user whos created the article.
var user = new UserSchema({
email : 'asdf#gmail.com',
nick : 'danilo'
...
});
user.save(function(error) {
var article = new ArticleSchema({
title : 'title',
alise : 'asdf',
user : user,
...
});
article.save(function(error) {
if(error) {
console.log(error);
}
});
}
And to find an article that was created for danilo:
ArticleSchema
.find(...)
.populate({
path: 'user',
match: { nick: 'danilo'},
select: 'email nick -_id'
})
.exec()
I suggest you to read about mongoose populate here

Answer 2

As of 4.5.0 You can use populate virtuals : http://mongoosejs.com/docs/populate.html#populate-virtuals
UserSchema = new db.Schema({
email: {type: String, required: true},
pass: {type: String, required: true},
nick: {type: String, required: true},
admin: {type: String, default: ''},
reg: {type: Date, default: Date.now}
});
ArticleSchema = new db.Schema({
title: {type: String, required: true},
alise: {type: String},
time: {type: Date, defaults: Date.now},
view: {type: Number, defaults: 0},
author: {type: String},
content: {type: String},
classes: {type: db.Schema.Types.ObjectId, ref: 'Classes'},
user: {type: String}
});
ArticleSchema.virtual('_user', {
ref: 'User', // The model to use
localField: 'user', // Find people where `localField`
foreignField: 'email', // is equal to `foreignField`
// If `justOne` is true, 'members' will be a single doc as opposed to
// an array. `justOne` is false by default.
justOne: true,
options: { sort: { name: -1 }, limit: 5 }
});
var User = mongoose.model('User', UserSchema);
var Article = mongoose.model('Article', ArticleSchema);
Article.find({}).populate('_user').exec(function(error, articles) {
/* `articles._user` is now an array of instances of `User` */
});