Models & Schemas

Models & Schemas

Before saving data to MongoDB, you need to define the shape of your data. Mongoose is an ODM (Object Data Modeling) library that provides schemas and models — a structured way to define what your data looks like, validate it, and interact with MongoDB.

Installing Mongoose

npm install mongoose

What Is a Schema?

A schema defines the structure of a document in a MongoDB collection — the fields, their data types, validation rules, and default values.

Creating a Schema

// models/ninja.js
const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const ninjaSchema = new Schema({
    name: {
        type: String,
        required: [true, 'Name is required'],
        trim: true,
    },
    rank: {
        type: Number,
        required: [true, 'Rank is required'],
        min: [1, 'Rank must be at least 1'],
        max: [10, 'Rank cannot exceed 10'],
    },
    available: {
        type: Boolean,
        default: false,
    },
}, { timestamps: true });

const Ninja = mongoose.model('Ninja', ninjaSchema);
module.exports = Ninja;

Schema Types

Type	JavaScript Equivalent	Example
String	string	"Ryu"
Number	number	5
Boolean	boolean	true
Date	Date object	new Date()
Array	array	["stealth", "combat"]
ObjectId	MongoDB ID	Reference to another document

Validation Options

Option	Applies To	Purpose
required	All types	Field must have a value
min / max	Number, Date	Value range limits
minlength / maxlength	String	Character count limits
enum	String	Restrict to specific values
match	String	Must match a regex pattern
default	All types	Default value if not provided
trim	String	Remove leading/trailing whitespace

The timestamps Option

{ timestamps: true }

This automatically adds createdAt and updatedAt fields to every document. Mongoose manages these — createdAt is set when the document is created, and updatedAt is refreshed on every save.

What Is a Model?

const Ninja = mongoose.model('Ninja', ninjaSchema);

A model is a constructor compiled from a schema. It provides methods for creating, reading, updating, and deleting documents in the corresponding MongoDB collection. The first argument ('Ninja') becomes the collection name (lowercased and pluralized: ninjas).

Key Takeaways

• Mongoose schemas define the structure, types, and validation rules for MongoDB documents
• Models are constructors that provide CRUD methods for interacting with collections
• Built-in validators include required, min, max, enum, and match
• timestamps: true automatically tracks creation and modification dates