What hook to alter the result of a view?

Question

In a custom module, I have a custom entity for which a view shows the following values:

Contact is the ID of another entity (Person) containing some fields, such as Email. Adresse courriel is a Custom text field defined in the view.

What hook should I use to achieve the following task?

1. Query the Person entity with the Contact value to retrieve the Email field value
2. Update Adresse courriel in the view output

Answer 1

1- Firstly you need to add a relationship to the Person entity to have the fields available.

2- then use hook_views_query_alter() to change the fields values.

Answer 2

I added this to MemberViewsData.php:

class MemberViewsData extends EntityViewsData
{
  /**
   * {@inheritdoc}
   */
  public function getViewsData()
  {
    $data = parent::getViewsData();

    // Additional information for Views integration, such as table joins, can be
    // put here.
    $data['member']['contact_id'] = array(
      'title' => t('Contact Id'),
      'relationship' => array(
        'base' => 'person',
        'base field' => 'id',
        'handler' => 'views_handler_relationship',
        'label' => t('Member to Person (Contact)'),
        'title' => t('Person (Contact)'),
        'id' => 'standard',
      ),
    );
    return $data;
  }
}

Then I could use Views UI, adding a 'Relation' from Member (main entity of my view) to Person. And here it is: