Model Aggregate

Combine Models with Aggregate Class.

Introduction

We previously saw how Aggregate class work, also we had a pretty good look at the Model class as well, now let's see how we can combine them together.

Model Aggregate Class

Each model by default has an aggregate method which returns an instance of ModelAggregate class, this class extends the Aggregate class and adds some useful methods to to, also it manipulates it to match the model nature and behavior.

Example of usage

Let's say we have a User model, and we want to get the average age of all users.

src/models/user.ts

import { Model } from "@mongez/monpulse";

export class User extends Model {
  /**
   * {@inheritDoc}
   */
  public static collection = "users";
}

Now let's use the aggregate method to get the average age of all users.

src/index.ts

import { User } from "./models/user";

const users = await User.aggregate().where("age", ">", 18).get();

console.log(users);

Unlike the base Aggregate class, the ModelAggregate's get method returns an array of models instead of plain objects, so we can use the model methods on the returned documents.

If yoy want to override the returned model, pass the first argument with a callback to the get method.

const users = await User.aggregate()
  .where("age", ">", 18)
  .get((user) => {
    return {
      ...user,
      fullName: `${user.firstName} ${user.lastName}`,
    };
  });

This would return an array of objects with the fullName property, but not an instance of User model.

Return first model

To return the first model, we can use the first method.

const user = await User.aggregate().where("age", ">", 18).first();

Pagination

Pagination works exactly like normal Aggregate.paginate method but the returned documents are instances of the model.

const { documents: users, paginationInfo } = await User.aggregate()
  .where("age", ">", 18)
  .paginate(1, 10);

Chunk

Chunk method is also available, it works exactly like the Aggregate.chunk method but the returned documents are instances of the model.

await User.aggregate().where("age", ">", 18).chunk(10, (users) => {
  console.log(users);
});