Module development and code questions

Drupal redirects to /core/install.php when I try to open page including a SQLite query

I have a Drupal site on a web server. On one page of the site, I want to print out information from a sqlite database. But if I enter the url to the page, I get redirected to /core/install.php

I integrated the database into the /sites/defualt/settings.php with the following code:

$databases['external']['default'] = [
'driver' => 'sqlite',
'database' => '/gesamtausgabe_2019.sqlite',
];

In FillPDF, class FillPdfFormField extends ContentEntityBase. The method ::baseFieldDefinitions() uses BaseFieldDefinition::create() to create a bunch of fields. I need to write an update hook to change one of these from type string to string_long.

I am trying to figure out why something weird is happening. I have the following in my_module.routing.yml:

my_module.test:
  path: '/my-module/test'
  defaults:
    _controller: '\Drupal\my_module\Controller\TestController::view'
    _title_callback: '\Drupal\my_module\Controller\TestController::getTitle'
  requirements:
    _permission: 'access content'

My Controller class is this:

Hey, there!

Is it always necessary to do a dependency injection for a service within a class if we will only use that service once inside the class? According to the Drupal documentation, is that recommended, but for practical purposes, is that useful?

 I have custom table having thousands of rows. I want to send the emails to the users by fetching the data from rows at specific time.
i am using Cron job but issue is this ---- timeout issue occurs. As fetching the thousands of rows and manipulate the data takes too much time. Can any one help me ? is there any way to use queue with cron.
thanks ..