Node + Mongoose: Populate array of ref objects

Question

I need to populate the comments based off of their ID's which are saved in another schema == Project as the array of comments.

Project

const projectSchema = new mongoose.Schema({
    user: { type: mongoose.Schema.Types.ObjectId, required: true, ref: 'User' },
    title: { type: String, required: true },
    description: { type: String, required: true, minLength: 200, maxlength: 500 },
    // comments: { type: Array, default: [], ref: 'Comment' },
    comments: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Comment' }],
})

Comment:

const commentSchema = new mongoose.Schema({
    comment: { type: String, required: true },
    project: { type: String, required: true, ref: 'Project' },
    user: { type: String, required: true, ref: 'User' }
)}

What do I want?

I want to populate and comments on a particular project.. This is what I am doing and it is returning null:

router.get('/:projectId', currentUser, authenticate, async (req: Request, res: Response) => {
    // search the project 
    const project = await Project.findById(req.params.projectId).populate('comment')
    // return the populated comments 
    console.log('THE LIST OF PROJECT', project)  // <-------- null
    res.send(project)
})

Answer 1

try this project schema

  const projectSchema = new mongoose.Schema({
      user: { type: mongoose.Schema.Types.ObjectId, required: true, ref: 'User' },
      title: { type: String, required: true },
      description: { type: String, required: true, minLength: 200, maxlength: 500 },
      comments: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Comment' }]
    });

and use 'comments' while populating

const project = await Project.findById(new mongoose.Types.ObjectId(req.params.projectId)).populate('comments')