Drupal 8.x

I’m trying to create a dynamic query, the query logic conditions needed are: AND, and OR.

The main query will include two sub queries.

The ConditionInterface::condition documentation states that:

“If called with 1 parameter, it should be a ConditionInterface that in itself forms a valid where clause. Use e.g. to build clauses with nested AND's and OR's.”

I'm having trouble understanding the implementation of conditionGroupFactory in my dynamic query.

I've tried two methods of implementing:

$connection = \Drupal::database();

$result = $connection->select('inventory', 'inv');

$result->fields('inv', ['part_number']);

$result->condition('inv.visable', 1);

I have a field that exists on nodes that have already been translated.

We recently decided we want that field translatable as well but by setting it to be translatable, it wipes out all the content for the translated versions of that field.

Is there a way or (patch) to prevent this?

Hello,
I want to create a slideshow of a number of images in the contents region 
of the front page of my Drupal8 system (running Debian 9, MySQL, PHP 7.2, and 
Apache2.4). 
To this end I followed the steps described in the tutorial under 
https://www.ostraining.com/blog/drupal/drupal-8-slideshows/:
(1) installed the required modules/plugins into the respective module and libraries 

Hello there, I got the following error message while trying to upgrade foirmDrupal 7 to Drupal 8. Could anyone please let me know how to solve this issue?

An AJAX HTTP error occurred.
HTTP Result Code: 504
Debugging information follows.
Path: /batch?id=2&op=do_nojs&op=do
StatusText: Gateway Timeout
ResponseText: 
504 Gateway Timeout
Gateway Timeout
The gateway did not receive a timely response
from the upstream server or application.

Thanks ana di welcome any suggestions you may have to successfully migrate a D 7 site to D8.

Regards