Convex vs. MongoDB

What is MongoDB?

MongoDB was released in 2009 to offer a flexible document store for developers to quickly build without SQL or schemas. It's evolved in many ways, eventually providing transactional support, materialized views, and other features that you would expect from a database product. They became source-available in 2018.

At a surface level, there are some similarities between the document storage structure of MongoDB and Convex, but we'd like to go over the differences to help people understand the product differences.

For clarity, MongoDB Community Server is their free, self-hostable version and MongoDB Atlas is a paid, hosted version of Community Server.

What’s similar?

Both Convex and MongoDB:

• Store data in documents
• Don’t use SQL
• Have hosted and self-hosted offerings
• Come with native vector search
• Allow schema-free development

What’s different?

Transactions and ACID compliance

Convex is a fully transactional data store, even though it’s a document store. It was built to be completely ACID compliant, much like a traditional RDBMS, without any performance compromises.

MongoDB is atomic on the document level, but requires you to manually configure two-phase commit transactions for operations that affect multiple documents at once. Their API for enabling transactions can be found here. Performance is affected when using their transactions API, removing a lot of the benefit of using a NoSQL database.

Reactivity / Realtime

Convex’s database offers realtime capabilities by default with automatic subscriptions for functions. There is no setup or middleware required to configure it. Convex’s websocket client provides consistency guarantees that are not possible when your reads are on a different channel than your writes.

MongoDB is rolling out support for realtime subscriptions with your applications using their Realm Web SDK, which is in the Preview stage as of writing this.

Product Offering

Convex is a backend-as-a-service which comes with a database, file storage, cron jobs, and other features to write your entire backend directly in TypeScript.

MongoDB is a document store/database. You need other products for the rest of your backend.

GUI

Convex offers a builtin GUI that lets you test functions, edit data directly, and view logs all from within your web browser. It’s a large part of the development experience.

MongoDB Atlas provides a GUI to edit documents. MongoDB Community Server requires you to install MongoDB Compass to visualize your data.

Type Safety

Convex provides end-to-end type safety from code to client, direct type inference, and autocompletion out of the box. Convex allows you to define schemas at the database and application level in pure TypeScript.

MongoDB is a largely untyped document store that leans on external ORMs to define schemas at the application level. ORMs don’t provide end-to-end type safety.

Query Language

Convex doesn’t use a query language for accessing your data. When writing query functions, you can use our native DB interface to filter and add operators.

import { query } from "./_generated/server";
import { v } from "convex/values";

// Return the last 100 tasks in a given task list.
export const getTaskList = query({
  args: { taskListId: v.id("taskLists") },
  handler: async (ctx, args) => {
    const tasks = await ctx.db
      .query("tasks")
      .filter(q => q.eq(q.field("taskListId"), args.taskListId))
      .order("desc")
      .take(100);
    return tasks;
  },
});

MongoDB uses their own language, MQL. Once you learn MQL, you can use operators to manipulate your data.

Actions

Convex has a native wrapper for external APIs called Actions, ensuring that third-party software doesn’t affect your database performance.

MongoDB does not have a native wrapper for interacting with external APIs.

Auth

Convex integrates with the standard set of external auth providers and does not have a native auth provider.

MongoDB provides standard auth methods with external providers and lets you define RBAC rules for restricting access within organizations.

Pricing

Convex has a free developer plan with resource and member limits. Convex Pro has a flat fee per seat on the Professional plan, with additional charges for exceeding limits. Convex has an open-source offering that you can self-host.

MongoDB Atlas has a free plan for testing and Pro/Enterprise plans. They also have their Enterprise Server product available as a download for self-hosting, but in their words, it’s only meant for evaluation and development purposes. MongoDB Community Server is free, but has no vector search, no monitoring, no built-in GUI, and no on-call technical support.

Resource limits are higher and lower in different areas for both projects, compare them here:

• Convex’s Pricing
• MongoDB’s Pricing