# Load smart fields using hook

This example shows you how to implement an afterFind hook with Sequelize to load several smart fields at once when a record is retrieved from the database. Learn more about [Sequelize hooks](https://sequelize.org/master/manual/hooks.html).

The main advantage of using an afterFind hook is that it allows you to avoid multiplying queries to your database if those queries are redundant when retrieving smart fields values.\
\
Here a **Program** `hasMany` **Activities**. \
\
We want to display two smart fields:  

* `"hasActivity"`, that will return whether the program has any related activities in the database.
* `"duration"`, that will return the length of the program in weeks.

![](https://2793709227-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-M0vHiS-1S9Hw3djvoTw%2F-M5bjruEem8301lQXTrX%2F-M5bk8GXM43J3_dQMsLz%2Fload-smart-fields-hooks.png?alt=media\&token=5861ad1a-a8fd-4d90-a78f-a54c6a5c6036)

## Requirements

* An admin backend running on forest-express-sequelize

## How it works

### Directory: /models

This directory contains the `programs.js` file where the model is declared. 

As Sequelize hooks are declared upon the model definition, the afterFind hook is implemented in this file.

{% tabs %}
{% tab title="programs.js" %}

```javascript
function calculateNumberOfWeek({ startDate, finishDate }) {
  const diff = startDate - finishDate;
  const diffInWeeks = (diff / (1000 * 60 * 60 * 24 * 7));
  return Math.abs(Math.round(diffInWeeks));
}

module.exports = (sequelize, DataTypes) => {
  const { Sequelize } = sequelize;
   const Programs = sequelize.define('programs', {
    startDate: {
      type: DataTypes.DATE,
    },
    finishDate: {
      type: DataTypes.DATE,
    },
    description: {
      type: DataTypes.STRING,
    },
  }, {
    tableName: 'programs',
    underscored: true,
    timestamps: false,
    schema: process.env.DATABASE_SCHEMA,
    hooks: {
      afterFind: async (programs) => {
        // Check if several records have been fetched or a single one
        const isFindOne = !programs.length;
        if (isFindOne) { programs = [programs]; }
        const recordsIds = programs.map(record => record.id);
        const activities = await sequelize.models.activities.findAll({
          where: { programIdKey: recordsIds },
        });

        programs.forEach((program) => {
          program.duration = calculateNumberOfWeek(program);
          program.hasActivity = activities.some(activity => activity.programIdKey === program.id);
        });

        return isFindOne ? programs[0] : programs;
      },
    },
  });
```

{% endtab %}
{% endtabs %}

### Directory: /forest

This directory contains the `programs.js` file where the smart fields `duration` and `hasActivity` are declared. 

{% hint style="info" %}
As the logic to retrieve the field value is defined in the hook, you do not need to define the get method for each smart field.
{% endhint %}

{% code title="/forest/programs.js" %}

```javascript
const { collection } = require('forest-express-sequelize');

collection('programs', {
  actions: [],
  fields: [
    {
      field: 'duration',
      type: 'Number',
    }, {
      field: 'hasActivity',
      type: 'Boolean',
    }
  ],
  segments: [],
});
```

{% endcode %}