mongoose-tsgen

mongoose-tsgen

A plug-n-play Typescript interface generator for Mongoose.

• Motivation
• Features
• Compatibility
• Installation
• The Gist
• Usage
• Example
• Development

Motivation

Using Mongoose with Typescript requires duplicating Mongoose Schemas using Typescript interfaces (see this post by the Mongoose creator). To avoid duplication, libraries such as typegoose & ts-mongoose have sprouted up which define a custom schema syntax that is used to generate both the Mongoose Schemas and the Typescript interfaces. Unfortunately, this requires users to completely rewrite their Mongoose Schemas using an unfamiliar and less-supported syntax than Mongoose itself.

This library aims to remove these drawbacks by instead parsing your already-written Mongoose Schemas and generating associated Typescript interfaces. This removes the need to learn a whole new library and makes this library extremely simple to integrate into an existing Mongoose project.

Features

• Automatically generate Typescript typings for each Mongoose document, model and subdocument
• Works out of the box, don't need to rewrite your schemas
• Includes a "Mongoose-less" version of each schema interface (Mongoose typings removed)

Compatibility

• All Mongoose types, arrays and maps
• Virtual properties
• Mongoose method, static & query functions
• Multiple schemas per file
• Typescript path aliases

Mongoose version

Find your Mongoose version below and install the associated mongoose-tsgen version. Ensure to refer to each version's respective README for documentation (hyperlinked in table).

mongoose	mongoose-tsgen
5.11.19+	latest
5.11.0-5.11.18	7.1.3
<5.11.0	6.0.10

Installation

mongoose-tsgen can be installed globally or locally as a dev dependency. Refer to the table above to ensure you are using the correct version.

# install as dev dependency with npm
npm install -D mongoose-tsgen

# install mongoose-tsgen v7.1.3 for mongoose v5.10.19 (see table above for compatibility)
npm install -D mongoose-tsgen@7.1.3

# install as dev dependency with yarn
yarn add -D mongoose-tsgen

The Gist

Once you've generated your typings file (see Usage), all you need to do is use the generated types in your schema definitions and throughout your project.

user.ts before:

import mongoose from "mongoose";

const UserSchema = new Schema(...);

export const User = mongoose.model("User", UserSchema);
export default User;

user.ts after:

import mongoose from "mongoose";
import { UserDocument, UserModel, UserQueries, UserSchema } from "../interfaces/mongoose.gen.ts";

const UserSchema: UserSchema = new Schema(...);

export const User: UserModel = mongoose.model<UserDocument, UserModel, UserQueries>("User", UserSchema);
export default User;

Then you can import the typings across your application from the Mongoose module and use them for document types:

import { UserDocument } from "./interfaces/mongoose.gen.ts";

async function getUser(uid: string): UserDocument {
  // user will be of type User
  const user = await User.findById(uid);
  return user;
}

async function editEmail(user: UserDocument, newEmail: string): UserDocument {
  user.email = newEmail;
  return await user.save();
}

Note that this practice is well documented online, I've found the following two Medium articles especially useful:

• Complete guide for Typescript with Mongoose for Node.js
• Strongly typed models with Mongoose and TypeScript

Usage

mtgen [MODEL_PATH]

Generate a Typescript file containing Mongoose Schema typings.

If you run into unknown type issues, check your Mongoose version. For Mongoose v5.11+, ensure you have removed the deprecated community typings @types/mongoose.

USAGE
  $ mtgen [MODEL_PATH]

OPTIONS
  -c, --config=config     [default: ./] Path of `mtgen.config.json` or its root folder. CLI flag
                          options will take precendence over settings in `mtgen.config.json`.

  -d, --dry-run           Print output rather than writing to file.

  -h, --help              Show CLI help

  -i, --imports=imports   Custom import statements to add to the output file. Useful if you use
                          third-party types in your mongoose schema definitions. For multiple imports,
                          specify this flag more than once.

  -o, --output=output     [default: ./src/interfaces] Path of output file to write generated typings.
                          If a folder path is passed, the generator will create a `mongoose.gen.ts` file
                          in the specified folder.

  -p, --project=project   [default: ./] Path of `tsconfig.json` or its root folder.

  --debug                 Print debug information if anything isn't working

  --no-format             Disable formatting generated files with prettier.

  --no-mongoose           Don't generate types that reference mongoose (i.e. documents). Replace ObjectId with
                          string.

  --no-populate-overload  Disable augmenting mongoose with Query.populate overloads (the overloads narrow
                          the return type of populated documents queries).

Specify the directory of your Mongoose schema definitions using MODEL_PATH. If left blank, all sub-directories will be searched for models/*.ts (ignores index.ts files). Files found are expected to export a Mongoose model.

See code: src/index.ts

Configuration File

All CLI options can be provided using a mtgen.config.json file. Use the --config option to provide the folder path containing this file ("./" will be searched if no path is provided). CLI options will take precendence over options in the mtgen.config.json file.

mtgen.config.json

{
  "imports": ["import Stripe from \"stripe\""],
  "output": "./src/custom/path/mongoose-types.ts"
}

Query Population

Any field with a ref property will be typed as RefDocument["_id"] | RefDocument. As part of the generated file, mongoose will be augmented with Query.populate overloads to narrow return types of populated queries (this can be disabled using the --no-populate-overload flag). A helper type IsPopulated and a type guard function PopulatedDocument will also be generated to help with handling populated documents, see usage below:

import { IsPopulated, PopulatedDocument } from "../interfaces/mongoose.gen.ts";

// UserDocument["bestFriend"] = mongoose.Types.ObjectId | UserDocument
function unsafeType(user: UserDocument) {
  // type guard
  if (IsPopulated(user.bestFriend))) {
    // user.bestFriend is confirmed to be populated, typescript will allow accessing its properties now
    console.log(user.bestFriend._id)
  }
}

// `user` is typed as a UserDocument with `bestFriend` populated
function safeType(user: PopulatedDocument<UserDocument, "bestFriend">) {
  console.log(user.bestFriend._id)
}

// due to the `Query.populate` overload, `user` will be typed as `PopulatedDocument<UserDocument, "bestFriend">`
// rather than the usual `UserDocument`
const user = await User.findById(uid).populate("bestFriend").exec()

// completely typesafe
safeType(user)

Example

./src/models/user.ts

import mongoose, { Schema } from "mongoose";
import { UserDocument, UserModel, UserSchema, UserQueries, UserObject } from "../interfaces/mongoose.gen.ts";

// UserSchema type
const UserSchema: UserSchema = new Schema({
  email: {
    type: String,
    required: true
  },
  firstName: {
    type: String,
    required: true
  },
  lastName: {
    type: String,
    required: true
  },
  metadata: Schema.Types.Mixed,
  bestFriend: {
    type: Schema.Types.ObjectId,
    ref: "User"
  },
  friends: [
    {
      uid: {
        type: Schema.Types.ObjectId,
        ref: "User",
        required: true
      },
      nickname: String
    }
  ],
  city: {
    coordinates: {
      type: [Number]
    }
  }
});

// NOTE: `this: UserDocument` is required for virtual properties to tell TS the type of `this` value using the "fake this" feature
// you will need to add these in after your first ever run of the CLI
UserSchema.virtual("name").get(function (this: UserDocument) {
  return `${this.firstName} ${this.lastName}`;
});

UserSchema.methods = {
  isMetadataString() {
    return this.metadata === "string";
  }
};

UserSchema.statics = {
  async getFriends(friendUids: UserDocument["_id"][]): Promise<UserObject[]> {
    return await this.aggregate([{ $match: { _id: { $in: friendUids } } }]);
  }
};

UserSchema.query = {
  populateFriends() {
    return this.populate("friends.uid", "firstName lastName");
  }
};

export const User = mongoose.model<UserDocument, UserModel, UserQueries>("User", UserSchema);
export default User;

generate typings

# run mongoose-tsgen
npx mtgen

generated typings file ./src/interfaces/mongoose.gen.ts

import mongoose from "mongoose";

export interface UserFriend {
  uid: User["_id"] | User;
  nickname?: string;
  _id: mongoose.Types.ObjectId;
}

export type UserObject = User;

export type UserQueries = {
  populateFriends: <Q extends mongoose.Query<any, UserDocument, any>>(this: Q) => Q;
}

export type UserMethods = {
  isMetadataString: (this: UserDocument) => boolean;
}

export type UserStatics = {
  getFriends: (this: UserModel, friendUids: UserDocument["_id"][]) => Promise<UserObject[]>;
}

export interface UserModel extends mongoose.Model<UserDocument, UserQueries>, UserStatics {}

export type UserSchema = mongoose.Schema<UserDocument, UserModel>

export interface User {
  email: string;
  firstName: string;
  lastName: string;
  bestFriend?: User["_id"] | User;
  friends: UserFriend[];
  city: {
    coordinates: number[];
  };
  _id: mongoose.Types.ObjectId;
}

export interface UserFriendDocument extends mongoose.Types.EmbeddedDocument {
  uid: UserDocument["_id"] | UserDocument;
  nickname?: string;
  _id: mongoose.Types.ObjectId;
};

export interface UserDocument extends mongoose.Document<mongoose.Types.ObjectId, UserQueries>,
  UserMethods {
    email: string;
    firstName: string;
    lastName: string;
    metadata?: any;
    bestFriend?: UserDocument["_id"] | UserDocument;
    friends: mongoose.Types.DocumentArray<UserFriendDocument>;
    city: {
      coordinates: mongoose.Types.Array<number>;
    };
    name: string;
    _id: mongoose.Types.ObjectId;
  };

Development

• Cut down node_modules by using peer dependencies (i.e. mongoose) and stripping oclif.