Add links on Wordpress custom endpoint - wordpress

Question

I created a custom endpoint for specific data from a custom table in my Wordpress plugin. It get's all the data from the table with the getHelpers() function. After that it will be merged by some user data. I would like to add the profile_image as a link to the response so we can get it with the embed parameter.
What is the best way to add the link to the response? I know the $response->add_link() function but this would add it to the response and not to each contributor.
I tried to add the link as an array but this won't react on the _embed parameter.
This is my code for the custom endpoint:
class VEMS_Rest_Contributors extends WP_REST_Controller {
protected $namespace = 'vems/v2';
protected $rest_base = 'contributors';
/**
* Register the routes for coupons.
*/
public function register_routes() {
register_rest_route( $this->namespace, '/' . $this->rest_base, array(
'methods' => WP_REST_Server::READABLE,
'callback' => array( $this, 'get_items' ),
'args' => $this->get_collection_params(),
) );
}
public function get_items( WP_REST_Request $request ) {
$project_id = $request->get_param( 'project_id' );
$contributors = array();
if( !empty($project_id) ) {
$project = new VEMS_Project( $request['project_id'] );
$helpers = $project->getHelpers();
foreach($helpers as $helper) {
$contributor = array();
if( !empty($helper->contributor_id) ) {
$user = get_user_by( 'ID', $helper->contributor_id );
$user_meta = get_user_meta( $helper->contributor_id );
$contributor['ID'] = $helper->contributor_id;
$contributor['user_nicename'] = $user->data->display_name;
$contributor['user_profile_image'] = $user_meta['contributor_profile_image'][0];
} else {
$contributor['user_nicename'] = $helper->name;
$contributor['user_profile_image'] = $helper->image_id;
}
$contributor['item_total'] = $helper->item_total;
$contributor['checked'] = $helper->checked;
$contributor['helper_date'] = $helper->helper_date;
/*
$contributor['_links']['profile_image'] = array(
'href' => rest_url( '/wp/v2/media/' . $contributor['user_profile_image'] ),
'embeddable' => true
);
*/
$contributors[] = $contributor;
}
}
$response = rest_ensure_response( $contributors );
return $response;
}
public function get_collection_params() {
$params['project_id'] = array(
'description' => __( 'Limit result set to contributors assigned a specific project.', 'vems' ),
'type' => 'integer',
'sanitize_callback' => 'absint',
'validate_callback' => 'rest_validate_request_arg',
);
return $params;
}
}

Answer 1

to handle links on route vems/v2/contributors?_embed, the element profile_image must be an array of links and then you can do that
$contributor['_links']['profile_image'] = [
[
'href' => rest_url( '/wp/v2/media/' . $contributor['ID'] ),
'embeddable' => true,
],
];