Mongo Assert extends the functionality of Zod, integrated with the MongoDB Node.js driver, to provide a more intuitive and powerful way to validate and assert MongoDB documents.

Some of its features include:

Validation of unique fields
Validation of the integrity of references to other collections
Adherence to a Zod schema

But why?

Mongo Assert is something I put together out of frustration with existing, heavy handed solutions for MongoDB schema management. Mongo Assert is intended to have a minimal footprint, add on to existing validation infrastructure, and plug in seamlessly to build-time integrity checks.

Usage

Mongo Assert is available as an NPM package. To install it, run:

npm install mongo-assert
pnpm install mongo-assert
yarn add mongo-assert
bun install mongo-assert

Mongo Assert supports Zod schemas out of the box, so any schemas you may already have defined can be used with any MongoDB instance.

Examples

Getting started

For all of the examples below, we'll be using the following schema:

import { z } from 'zod';
import { ObjectId } from "mongo-assert/lib/mongodb"

export const userSchema = z.object({
    _id: ObjectId,
    name: z.string(),
    email: z.string().email(),
});

export type User = z.infer<typeof userSchema>;

Unique field validation

Mongo Assert extends Zod schemas to check that your documents match the desired schema. For example:

import MongoAssert, { type AssertUniqueType } from 'mongo-assert';
import { userSchema, type User } from "./schemas";

export const UserEmailsUniqueValidator: AssertUniqueType<User> = MongoAssert.unique.fromSchema(userSchema, ["email"]);

The returned object is a Zod schema that can be directly invoked to validate a result from MongoDB. This object is of the type:

type AssertUniqueType<T> = z.ZodEffects<z.ZodArray<z.ZodType<T>>, T[], unknown>;

And you can use it like this:

import { createMongoClient } from "./your-mongo-client";
import { UserEmailsUniqueValidator } from "./schemas";

const client = await createMongoClient(url, options);

async function main() {
    const users: WithId<Document>[] = await client.db("db").collection("users").find().toArray();

    try {
        return UserEmailsUniqueValidator.parse(users) satisfies User[];
    } catch (e) {
        console.error(e);
        return;
    }
}

Reference validation

Mongo Assert also supports validation of references to other collections.

For example, suppose we have a collection of Stores that must be associated to an existing User. Let's define our schema first:

import { z } from 'zod';

export const storeSchema = z.object({
    _id: ObjectId,
    name: z.string(),
    owner: z.string(),
    ownerEmail: z.string().email(),
});

export type Store = z.infer<typeof storeSchema>;

Now, we can define a reference validator between these two collections:

import MongoAssert from 'mongo-assert';

const StoresHaveOwnersValidator = new MongoAssert.relation({
    db: "your-db",
    mainCollection: "users",
    relationCollection: "stores",
    mainSchema: userSchema,
    relationSchema: storeSchema,
    relations: {
        "email": "ownerEmail"
    }
});

And then we can use it like this:

import { createMongoClient } from "./your-mongo-client";
import { StoresHaveOwnersValidator } from "./schemas";

const client = await createMongoClient(url, options);

async function main() {
    const stores: WithId<Document>[] = await client.db("db").collection("stores").find().toArray();

    try {
        return StoresHaveOwnersValidator.parse(stores) satisfies Store[];
    } catch (e) {
        console.error(e);
        return;
    }
}