strapi/docs/3.0.0-beta.x/guides/custom-data-response.md

# Custom data response

In this guide we will see how you can customize the data of your APIs responnses.

## Introduction

To be able to update the default data response you have first to understand how it works.

When you create a content type, it generate an API with the following list of [endpoints](../content-api/endpoint).

Each of these endpoint trigger a controller action. Here is the list of [controller actions](../concepts/controller.md) that exist by default when a content type is created.

If you check the controller file of your generated API `./api/{content-type}/controller/{Content-Type}.js`, you will see an empty file. It's because all the default logic is managed by Strapi. But we allow your override these functions with your own logic.

And that is what we will do to manage our custom data response.

## Example

In our example we will imagine we have restaurants with a chef. By default when you fetch restaurants, you will got all information of the chef.
And I don't want to be able to fetch the email - to respect the privacy of my chefs.

To do that, we will customize the functions that fetch all restaurants and remove the email of all restaurant's chef.

To follow my example your will have to create a content type `restaurant` and add the following field definition:

- `string` attribute named `name`
- `text` attribute named `description`
- `relation` attribute **Restaurant** (`chef`) - **User** has many **Restaurants** - **Users** (`restaurants`)

Then add some data.

## Override controller action

To customize the function that fetch all our restaurants we will have to override the `find` function.

First, to see the difference, let's request `GET /restaurants`. You will see all the data you created.
Now let's start the customization.

**Path —** `./api/restaurant/controller/Restaurant.js`

```js
module.exports = {
  async find() {
    return 'strapi';
  },
};
```

After saving the new function, let's restart the `GET /restaurants` request. We will see `strapi` as response.
So it works well.

## Get the data back

We now know the function we have to update, but we just want to customize the returned restaurant values.

In the [controller documentation](../concepts/controllers.html#extending-a-model-controller) you will find the default function of all actions. It will help you to not re-code all the logic to fetch your data.

**Path —** `./api/restaurant/controller/Restaurant.js`

```js
const { sanitizeEntity } = require('strapi-utils');

module.exports = {
  async find(ctx) {
    let entities;
    if (ctx.query._q) {
      entities = await strapi.services.restaurant.search(ctx.query);
    } else {
      entities = await strapi.services.restaurant.find(ctx.query);
    }

    return entities.map(entity =>
      sanitizeEntity(entity, { model: strapi.models.restaurant })
    );
  },
};
```

And now the data is back on `GET /restaurants`

## Apply our changes

We can see the `find` function `return` the result of the `map`. And the map function just sanitize all entries.

So instead of just return the sanitized entry, we will also remove the chef email of each restaurant.

**Path —** `./api/restaurant/controller/Restaurant.js`

```js
const { sanitizeEntity } = require('strapi-utils');

module.exports = {
  async find(ctx) {
    let entities;
    if (ctx.query._q) {
      entities = await strapi.services.restaurant.search(ctx.query);
    } else {
      entities = await strapi.services.restaurant.find(ctx.query);
    }

    return entities.map(entity => {
      const restaurant = sanitizeEntity(entity, {
        model: strapi.models.restaurant,
      });
      if (restaurant.chef && restaurant.chef.email) {
        delete restaurant.chef.email;
      }
      return restaurant;
    });
  },
};
```

And tada! The email disapeared.

::: tip
This guide can be applied to any other controller action.
:::