如何通过填充字段在猫鼬中查找文档？

Question

I have an issue with mongoose. When I make some field referenced to other collection, I lose ability to search by this field. I don't know how to describe my problem correctly, so look at the examples please.

Schema:

var PostSchema = new Schema({
title: String,
content: String,
url: String,
author: { type: Schema.ObjectId, ref: 'User'},
mainImage: String,
type: String
});

Query:

Post.find({author: user._id})
    .then(posts => res.send(posts))
    .catch(err => res.status(500).send(err))

Returns nothing. But if I change "author" field to String, it will works, but without populate. :(

Upd: I can't believe. I made this:

var PostSchema = new Schema({
title: String,
content: String,
url: String,
author: {type: String, ref: 'User'},
mainImage: String,
type: String
});

Just change type to string. Omg I can't figure out how it working. How mongoose knows which field I need to compare in ref collection? I mean there is no direct link to "_id" field (see query). Can someone explain?

Upd2:

Auhtor schema:

var UserSchema = new Schema({
id: String,
about: String,
firstname: String,
lastname: String,
email: String,
avatar: String,
city: String,
country: String,
dateOfBirth: String,
password: String,
},
{
  timestamps: true
})

As you can see, I using additional "id" field just in purpose to give users simple numeric id for url (/id1 etc). But I am sure this isn't the source of the problem :)

Answer 1

尝试改变type: Schema.ObjectId到type: mongoose.Schema.Types.ObjectId