Mongoose (MongoDB)/Cheat sheet

Contents

Your essential quick reference for using Mongoose — the elegant, schema-based ODM (Object Data Modeling) library for MongoDB and Node.js. 🍃🐍

It brings structure to your NoSQL chaos and makes working with MongoDB feel like magic.

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⚙️ Setup

Install Dependencies

npm install mongoose

Connect to MongoDB

import mongoose from "mongoose";

mongoose.connect("mongodb://localhost:27017/mydb")
  .then(() => console.log("✅ Connected to MongoDB"))
  .catch(err => console.error("❌ Connection failed", err));

With MongoDB Atlas:

mongoose.connect("mongodb+srv://user:pass@cluster0.mongodb.net/mydb?retryWrites=true&w=majority");

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🧱 Defining Schemas & Models

Basic Schema

import { Schema, model } from "mongoose";

const userSchema = new Schema({
  name: { type: String, required: true },
  email: { type: String, unique: true, required: true },
  age: Number,
  createdAt: { type: Date, default: Date.now },
});

const User = model("User", userSchema);

Schema Options

Example:

age: { type: Number, min: 18, max: 100 },
role: { type: String, enum: ["user", "admin", "guest"] },

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🧩 Creating Documents

Save a Document

const user = new User({ name: "Alice", email: "a@example.com" });
await user.save();

Create Shortcut

await User.create({ name: "Bob", email: "b@example.com" });

Insert Many

await User.insertMany([
  { name: "Tom" },
  { name: "Jerry" },
]);

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🔍 Reading Documents

Find All

const users = await User.find();

Find One

const user = await User.findOne({ email: "a@example.com" });

Find by ID

const user = await User.findById("66f4abc123...");

Query Filters

await User.find({ age: { $gte: 18, $lte: 30 } });
await User.find({ name: /bob/i }); // regex
await User.find().sort({ age: -1 }).limit(5).skip(10);

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✏️ Updating Documents

Update One

await User.updateOne({ name: "Alice" }, { age: 28 });

Update Many

await User.updateMany({ age: { $lt: 18 } }, { underage: true });

Find and Update

const updated = await User.findOneAndUpdate(
  { email: "a@example.com" },
  { name: "Alicia" },
  { new: true }
);

Save Changes

const user = await User.findById(id);
user.age = 30;
await user.save();

---

🗑️ Deleting Documents

await User.deleteOne({ email: "a@example.com" });
await User.deleteMany({ age: { $lt: 13 } });
await User.findByIdAndDelete("66f4abc...");

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🔗 Relationships (Population)

Define Reference

const postSchema = new Schema({
  title: String,
  content: String,
  author: { type: Schema.Types.ObjectId, ref: "User" },
});

const Post = model("Post", postSchema);

Populate Data

const posts = await Post.find().populate("author", "name email");

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🧩 Embedded Documents (Subdocuments)

const commentSchema = new Schema({
  text: String,
  date: { type: Date, default: Date.now },
});

const blogSchema = new Schema({
  title: String,
  comments: [commentSchema],
});

const Blog = model("Blog", blogSchema);

await Blog.create({
  title: "My Blog",
  comments: [{ text: "Great post!" }],
});

---

🧮 Aggregation Pipeline

const stats = await User.aggregate([
  { $match: { age: { $gte: 18 } } },
  { $group: { _id: null, avgAge: { $avg: "$age" } } },
]);

Common operators:

---

🧾 Query Operators

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🧰 Indexes

Create Index

userSchema.index({ email: 1 });

Unique Index

userSchema.index({ email: 1 }, { unique: true });

Compound Index

postSchema.index({ author: 1, createdAt: -1 });

---

🔒 Validation

const userSchema = new Schema({
  email: {
    type: String,
    required: true,
    validate: {
      validator: (v) => /@/.test(v),
      message: (props) => `${props.value} is not a valid email!`,
    },
  },
});

---

🔁 Middleware (Hooks)

Example:

userSchema.pre("save", function (next) {
  console.log("About to save:", this.name);
  next();
});

---

🧮 Virtuals

Computed properties not stored in the DB.

userSchema.virtual("info").get(function () {
  return `${this.name} (${this.email})`;
});

const user = await User.findOne();
console.log(user.info); // "Alice (a@example.com)"

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🧾 Transactions (with Sessions)

Requires MongoDB Replica Set or Atlas cluster.

const session = await mongoose.startSession();
session.startTransaction();
try {
  await User.create([{ name: "Alice" }], { session });
  await Post.create([{ title: "Post" }], { session });
  await session.commitTransaction();
} catch (err) {
  await session.abortTransaction();
}
session.endSession();

---

🧰 Utility

Count

await User.countDocuments({ active: true });

Distinct

await User.distinct("role");

Lean Queries (Faster, no Mongoose overhead)

await User.find().lean();

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⚡ Performance Tips

• Use .lean() for read-heavy operations.
• Always index frequently queried fields.
• Limit deep population — prefer multiple queries.
• Use bulkWrite() for mass updates.
• Avoid unbounded queries — always limit().
• Enable connection pooling for scalability.

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🧾 TL;DR Mind Map

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🍃 Fun Facts

• Mongoose was first released in 2010 and remains the most popular ODM for Node.js.
• It brings schema validation to MongoDB’s schema-less design.
• Mongoose models are like “smart wrappers” around collections — enforcing consistency.
• It even supports TypeScript out of the box via types!
• MongoDB + Mongoose = JSON’s happy place.