server/src/models/Card.js

import mongoose from "mongoose";
const cardSchema = new mongoose.Schema(
  {
    title: {
      type: String,
      required: true,
      trim: true
    },
    parentId: {
      type: mongoose.Schema.Types.ObjectId,
      default: null
    },
    order: {
      type: Number,
      default: 0
    }
  },
  {
    timestamps: true
  }
);
export const Card = mongoose.model("Card", cardSchema);