server/src/models/Entry.js

import mongoose from "mongoose";
const entrySchema = new mongoose.Schema(
  {
    cardId: {
      type: mongoose.Schema.Types.ObjectId,
      required: true,
      ref: "Card"
    },
    question: {
      type: String,
      required: true,
      trim: true
    },
    answer: {
      type: String,
      required: true
    },
    order: {
      type: Number,
      default: 0
    }
  },
  {
    timestamps: true
  }
);
export const Entry = mongoose.model("Entry", entrySchema);