I want to save user as object in rating object, but when I am going to add it its userId adding instead of whole user object ?

const reviewSchema = new mongoose.Schema(
  {
    name: {
      type: String,
      required: [true, "name is require"],
    },
    rating: {
      type: Number,
      default: 0,
    },
    comment: {
      type: String,
    },
    user: {
      type: mongoose.Schema.Types.ObjectId,
      ref: "Users",
      required: [true, "user require"],
    },
  },
  { timestamps: true }
);

This is the model of rating in which user object added.

   const user = await userModel.findById({ _id: req.user._id });
    console.log(user);
    // review object
    const review = {
      name: user.name,
      rating: Number(rating),
      comment,
      user,
    };

This is the controller function in which user has gotted from request.params._id, but when I am going to save user object only its ID is being saving in database.