45-Nodejs Course 2023: Database Models: Default Values

Let's move to another important section, which is the default value for the model, in that sense, we want to set initial values for the model, for example, we want to set the published column to be false if the column itself does not exist.

However, this should only be done in the create operation, not in the update operation as we might later want to remove that column from that certain document.

Now let's go and add it.

// src/core/database/model/model.ts
import { Document, ModelDocument } from "./types";

export default abstract class Model extends CrudModel {
  // ...
  /**
   * Define Default value data that will be merged with the models' data
   * on the create process
   */
  public defaultValue: Document = {};
}

We defined an empty object here which will be used to store the default values for the model.

Now let's update the save method to apply the default values.

// src/core/database/model/model.ts
import { Document, ModelDocument } from "./types";
import Is from "@mongez/supportive-is";import {
  areEqual,
  except,
  get,
  merge,
  only,
  set,
} from "@mongez/reinforcements";

export default abstract class Model extends CrudModel {
  // ...

  /**
   * Perform saving operation either by updating or creating a new record in database
   */
  public async save(mergedData: Document = {}) {
    this.merge(mergedData);

    // check if the data contains the primary id column
    if (this.data._id && !this.isRestored) {
      // perform an update operation
      // check if the data has changed
      // if not changed, then do not do anything
      if (areEqual(this.originalData, this.data)) return;

      this.data.updatedAt = new Date();

      await queryBuilder.update(
        this.getCollectionName(),
        {
          _id: this.data._id,
        },
        this.data,
      );
    } else {
      // creating a new document in the database
      const generateNextId =
        this.getStaticProperty("generateNextId").bind(Model);

      // check for default values and merge it with the data
      this.checkDefaultValues();

      // if the column does not exist, then create it
      if (!this.data.id) {
        this.data.id = await generateNextId();
      }

      const now = new Date();

      // if the column does not exist, then create it
      if (!this.data.createdAt) {
        this.data.createdAt = now;
      }

      // if the column does not exist, then create it
      if (!this.data.updatedAt) {
        this.data.updatedAt = now;
      }

      this.data = await queryBuilder.create(
        this.getCollectionName(),
        this.data,
      );
    }
  }

  /**
   * Check for default values
   */
  protected checkDefaultValues() {
    // if default value is empty, then do nothing
    if (Is.empty(this.defaultValue)) return;

    // merge the data with default value
    this.data = merge(this.defaultValue, this.data);
  }
}

We added in the create process a new method called checkDefaultValues which will be called before the data is saved to the database.

In this method, we checked if the default value property is empty, if it is, then we do nothing, otherwise, we merge the default value with the data.

The merge will merge data deeply, so if the data already has a column, then it will not be overridden.

Now let's give it a try!

// src/app/users/models/user.ts

import { Model } from "core/database";
import { Document } from "core/database/model/types";

export default class User extends Model {
  /**
   * Collection name
   */
  public static collectionName = "users";

  /**
   * {@inheritDoc}
   */
  public defaultValue: Document = {
    published: true,
  };
}

We added published column to be true by default.

Now let's create a new user and see what happens.

// src/app/users/routes.ts
import User from './models/user';

const user = await User.create({
  name: 'hasan',
});

console.log(user.data); // {id: 1, name: 'hasan', published: true, _id: '...', createdAt: '...', updatedAt: '...'}