CODEWITHSUNDEEP
node.jsmongoose
user824624
user824624

Reputation: 8056

can't populate the array with mongoose in node.js

This is my schema on the course

var CourseSchema = mongoose.Schema({
    students:[{ type: ObjectId, ref: 'User' }]
});
var CourseModel = mongoose.model('Course',CourseSchema);

var UserSchema = mongoose.Schema({ name:String})
var UserModel = mongoose.model('User',UserSchema);

In the mongodb, I have created the existing courses and users, and when the user want to participate the course, the user reference will be added to the students array in the course model.

Here is how I try to add the user reference to the students

function joinCourse(cid,uid,callback){
    var options = { new: false };   
    var uid = mongoose.Types.ObjectId(uid);
    CourseModel.findOneAndUpdate({'_id':cid},{'$addToSet':{'students':uid}},options,function(err,ref){
        if(err) {
            console.log('update joinCourse'.red,err);
            callback(err, null);
        }else{
            console.log('update joinCourse  '.green+ref);                 
            callback(null,ref);
        }
    })

}

when the above function is executed, the students array has the objectID or reference of the user. However, when I want to populate the students from the course model, it doesn't work. 

var id = mongoose.Types.ObjectId(id);
CourseModel.findById(id).populate('students').exec(function(err, users) { 
    if(err){callback(err, null);}
    else{
            //// users.length == undefined 
        console.log("findCourseStudentsById".green,users.length);
        callback(null, users);
    }      
})

I didn't find any problem on populate function, so I wonder is there something wrong with joinCourse function? so I change the function as

   courseModel.findCourseById(cid,function(err,course){
            if(err) next(err);       
        else{
            course.students.push({'_id': mongoose.Types.ObjectId(uid)});

                course.save(function (err) {
                 if (err) next(err); 

                });
            }
   })

but still the populate doesn't work. Note, I am using mongoose 3.6

Upvotes: 0

Views: 1683

Answers (1)

robertklep
robertklep

Reputation: 203231

populate populates the model instance, but the callback is passed the model instance on which you call populate, and not the populated data itself: 

CourseModel.findById(id).populate('students').exec(function(err, course) { 
  if(err){callback(err, null);}
  else{
    console.log("findCourseStudentsById".green, course.students.length);
    callback(null, course);
  }      
});

Upvotes: 2

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