how to create a database schema (or model) with mongoose

19 Aug, 2025

Step 1: Initialize a Node.js Project

First, we need to create a Node.js project if you haven't done so already. Run the following command in your terminal:

npm init -y

step 2: install the mongoose and mongodb package by running

npm install mongoose mongodb

Now that we have succesfully installed the package we have to define (or bring it) into our app.

You must have a MongoDB server running on your machine (either directly installed, in a Docker container, etc.)

# index.js
//Now we coonect to the server
mongoose
  .connect("mongodb://localhost:27017/expense-tracker")
  .then(() => console.log("Database connected successfully!"))
  .catch((err) => console.error("Database connection error:", err));

step 3: let's define our data-base schema

First, we must understand what a schema is; A schema is simply like a blueprint where we organize our data, A place to slide in information in a structured way.

Now back to defining our data base schema // we will be creating a schema for an expense tracker API

//import the mongoose library
const mongoose = require("mongoose");

//lets name how db structure **ExpenseSchema**
const ExpenseSchema = new mongoose.Schema({
  // now we shall create a custom headings and rules for filling body

  decription: {
    type: string,
    required: true,
  },
  amount: {
    type: Number,
    required: true,
  },
  category: {
    type: string,
    enum: [
      "Groceries",
      "Leisure",
      "Electronics",
      "Utilities",
      "Clothing",
      "Health",
      "Others",
    ],
    required: true,
  },
  date: {
    type: Date,
    default: date.now,
  },
});

Let's break this down:

type: String, Number, Date: These lines enforce the data type for each field. This is crucial for preventing errors and ensuring your data is predictable.

required: true: This is a simple but powerful rule. It ensures that no expense can be saved to our database without a value for that field.

enum: The enum property is our guardrail. It restricts the category to a specific list of strings we've defined. This keeps our data clean and consistent.

default: This property automatically assigns a value if one isn't provided. For the date field, we're automatically setting the date to the current time.

step 4: populating our database using model

//we need to create a model of our ExpenseScehema

const Expense = mongoose.model("Expense", ExpenseSchema);
//This model is now our gate way to the collection of data in our db

const newExpense = new Expense({
  description: "airtime purchase",
  amount: 35.0,
  category: "Subscription",
});

newExpense.save(); // This line saves the new expense to the database

congratulations you can now create and populate a schema into mongodb with mongoose