Loopback belongsTo relation with MongoDB giving Error 400 - mongodb

Question

In my MongoDB database, I have this data :
In a User collection :
{
"_id" : ObjectId("5a2c725621691170792fbc3e"),
"username" : "username",
"email" : "test#gmail.com"
}
In a Content Collection :
{
"_id" : ObjectId("5a2c7857b4f9e44a4d618bfd"),
"title" : "Article title",
"author" : ObjectId("5a2c725621691170792fbc3e")
}
So I've made 2 models in Loopback with a relation hasMany/belongsTo :
{
"name": "user",
...
"properties": {
"username": {
"type": "string",
"required": true
},
"email": {
"type": "string",
"required": true
}
},
"relations": {
"contents": {
"type": "hasMany",
"model": "content",
"foreignKey": "author"
}
}
}
Content has an author :
{
"name": "content",
"properties": {
"title": {
"type": "string",
"required": true
}
},
"relations": {
"author": {
"type": "belongsTo",
"model": "user",
"foreignKey": "author"
}
},
}
So that's great, Loopback give me those URLS :
/users/{id}/contents to get Contents of an user, it's working fine
/contents/{id}/author
to get the Author of a content, but this one give me an error :
400 Key mismatch: content.author: function () { [native code] },
user.id: 5a2c725621691170792fbc3e
I can't figure out what's wrong, thanks !

Answer 1

I set up an empty project and added models and relations like described and it works to get contents through user and user through content.
In you example data I see that author in content has a different value than id in user. Is that a typo in the question here or in the actual data?
"_id" : ObjectId("5a2c725621691170792fbc3e")
"author" : ObjectId("5a2c7af721691170792fbfd3")