Module

For the examples, here we use the module simple_analytics as example.
Module name : simple_analytics
Configuration object: simple_analytics.settings

Settings and mapping files structure.

Drupal 8 embedded with a configuration system which allow users to store variables in the database and usable in site wide as variables in drupal 7. Intend of use variable_set variable_get variable_del, in drupal 8 use Configuration API.

To make a redirection after user login, we can use the hook hook_user_login().
Note : You cannot use $form_state->setRedirectUrl() directly in the form alter, since it will be overwritten by UserForm::submitForm().

Check module exist

if (\Drupal::moduleHandler()->moduleExists('my_module')) {
    $message = 'Module exist.';
}
else {
    $message = 'Not exists.';
}
 

Step 1. Create a custom module and add the HOOK hook_views_data_alter(&$data). Here module : mymodule

Step 2.

Example :

$result =  array(
  '#markup' => 'Hello. This is my First Page',
);
$renderer = \Drupal::service('renderer');
$html = $renderer->render($result);

Search API and Database Search server.

1. Uninstall drupal basic Search
2. Install search_api and search_api_db
  NOTE : You can also use another database configures on settings.php
3. Add a Search Server (/admin/config/search/search-api/add-server).

Hook Update Deploy Tools is a great contrib module help to make most of site deploy operations programmatically.
Link : https://www.drupal.org/project/hook_update_deploy_tools