Mongoose referenced lookup collection field returned null in results

[OlammieAO]

I greet everyone Happy New Year in advance. Please I have this mongoose aggregate that returns the right records but do not include fields in the lookup collection i.e referenced collection.

******THIS IS MY SCHEMAS

===============USERS COLLECTION

const usersSchema = mongoose.Schema(
  {    
        fullname: {
        type: String,
        required: [true, 'First Name cannot be empty'],
        trim: true,
        index: true,
      },             
    email: {
      type: String,
      validate: [validator.isEmail, 'Provide a valid email'],
      trim: true,
    },
   password: {
      type: String,
      required: [true, 'Password is required'],
      },
}, {
  timestamps: true,
},
 
);

const Users = mongoose.model('User', usersSchema);
module.exports = Users;

===============MOTORS COLLECTION

const sub_origin_info_schema = mongoose.Schema({

  sub_garrage_user1: { //It is an object ID of users collection
    type: String,      
    required: false,     
  },
  garrage_name1: {
    type: String,      
    required: false,     
  },
sub_garrage_user2: { //It is an object ID of users collection
    type: String,      
    required: false,     
  },
  garrage_name2: {  
    type: String,      
    required: false,     
  },

  })

const motorSchema = new mongoose.Schema(
 {
    user_id:{ 
        type: { type: Schema.Types.ObjectId, ref: 'User'},
    },
garrage_of_origin_user:{ //It is an object ID of users collection
        type: String,
        required: true,
    },

    motor_code: {
        type: String,            
        required: true,
        unique: true,
    },       
    motor_name: {
        type: String,            
        required: true,
    },
    motor_number: {
        type: String,            
        required: true,
    },
    imo_number: {
        type: String,            
        required: true,
    },
    garrage_of_origin: {
        type: String,            
        required: true,
    },
journey_date: {
        type: String,            
        required: true,
    },

sub_origin_garage: sub_origin_info_schema,

    }, 
 {
    timestamps: true,
  },
);

const Motors = mongoose.model('Motor', motorsSchema);
module.exports = Motors;

*******WHAT I WANT TO ACHIEVE

The query worked but does not work as perfectly. It doesn't include the fullname and email of the referenced Collection using the field mentioned.

I want to achieve two things,

1.) I want to pull the user details(fullname and email) from the Users collection using the garrage_of_origin_user field in the Motors schema collection. The query worked but the fullname and email are null i.e they were not pulled.

How do I pull details(fullname and email) of the users in the subdocument sub_origin_garrage array object which are "sub_garrage_user1" and "sub_garrage_user2" fields? Note that there are users in the subdocuments(sub_origin_garage) too. How do i use lookup to pull out the fields in the users collection for this 3 users i.e garrage_origin_user, sub_garrage_user1 and sub_garrage_user2 in one document?

*******THIS IS MY CODE

Motor.aggregate([
      //{ $match : { '_id' : '674ed7fd61f952ddf3e4a661' } },
      { $unwind: "$sub_origin_garage" },
      { $unwind: "$sub_origin_garage.sub_garrage_user1" },
        { $match : 
          { $or: [ 
            { 'sub_origin_garage.sub_garrage_user1' : '6750838a51d231d3178343c7' },
            { 'sub_origin_garage.sub_garrage_user2' : '6750838a51d231d319656209' },   
       ]
        } 
      },
        { $sort : {journey_date: -1} },
                {
          "$lookup": {
              "from": "users",
              "localField": "garrage_of_origin_user",
              "foreignField": "_id",
              "as": "motorDriver"
          }
      },
      {   $project: {       
        motor_code: 1,
        motor_name: 1,
        motor_number: 1,
        imo_number: 1,
        garrage_of_origin: 1,
        journey_date: 1,
       'sub_origin_garage.garrage_name1': 1,
       'sub_origin_garage.garrage_name2': 1,
        motorDriver: { fullname: 1, email: 1 }
        }
    }
  
    ])
    .then(response => {

      res.status(200).json({
        status: 'success', 
           response      
      });     
    })
    .catch(error => {
        res.json({
            message: `An error occured!: ${error}`
        })
    })

I will appreciate your kind assistance.

[vkarpov15]

$lookup always returns an array, you would need an extra { $unwind: "$motorDriver" } before your final $project for this to work