Statics and Methods in TypeScript

You can define instance methods and static functions on Mongoose models. With a little extra configuration, you can also register methods and statics in TypeScript.

Methods

To define an instance method in TypeScript, create a new interface representing your instance methods. You need to pass that interface as the 3rd generic parameter to the Schema constructor and as the 3rd generic parameter to Model as shown below.

import { Model, Schema, model } from 'mongoose';

interface IUser {
  firstName: string;
  lastName: string;
}

// Put all user instance methods in this interface:
interface IUserMethods {
  fullName(): string;
}

// Create a new Model type that knows about IUserMethods...
type UserModel = Model<IUser, {}, IUserMethods>;

// And a schema that knows about IUserMethods
const schema = new Schema<IUser, UserModel, IUserMethods>({
  firstName: { type: String, required: true },
  lastName: { type: String, required: true }
});
schema.method('fullName', function fullName() {
  return this.firstName + ' ' + this.lastName;
});

const User = model<IUser, UserModel>('User', schema);

const user = new User({ firstName: 'Jean-Luc', lastName: 'Picard' });
const fullName: string = user.fullName(); // 'Jean-Luc Picard'

Statics

Mongoose models do not have an explicit generic parameter for statics. If your model has statics, we recommend creating an interface that extends Mongoose's Model interface as shown below.

import { Model, Schema, model } from 'mongoose';

interface IUser {
  name: string;
}

interface UserModel extends Model<IUser> {
  myStaticMethod(): number;
}

const schema = new Schema<IUser, UserModel>({ name: String });
schema.static('myStaticMethod', function myStaticMethod() {
  return 42;
});

const User = model<IUser, UserModel>('User', schema);

const answer: number = User.myStaticMethod(); // 42

Mongoose does support auto typed static functions now that it is supplied in schema options. Statics functions can be defined as following:

import { Schema, model } from 'mongoose';

const schema = new Schema(
  { name: String },
  {
    statics: {
      myStaticMethod() {
        return 42;
      },
    },
  }
);

const User = model('User', schema);

const answer = User.myStaticMethod(); // 42

Both Methods and Statics

Below is how you can define a model that has both methods and statics.

import { Model, Schema, HydratedDocument, model } from 'mongoose';

interface IUser {
  firstName: string;
  lastName: string;
}

interface IUserMethods {
  fullName(): string;
}

interface UserModel extends Model<IUser, {}, IUserMethods> {
  createWithFullName(name: string): Promise<HydratedDocument<IUser, IUserMethods>>;
}

const schema = new Schema<IUser, UserModel, IUserMethods>({
  firstName: { type: String, required: true },
  lastName: { type: String, required: true }
});
schema.static('createWithFullName', function createWithFullName(name: string) {
  const [firstName, lastName] = name.split(' ');
  return this.create({ firstName, lastName });
});
schema.method('fullName', function fullName(): string {
  return this.firstName + ' ' + this.lastName;
});

const User = model<IUser, UserModel>('User', schema);

User.createWithFullName('Jean-Luc Picard').then(doc => {
  console.log(doc.firstName); // 'Jean-Luc'
  doc.fullName(); // 'Jean-Luc Picard'
});