Have Database Update ignore prefix for multisite with shared database

Question

I currently have a multisite with a single database. Each instance has a different prefix for their tables, except for one with no prefix which is considered to be the main instance. Now there is a custom table I made that contains custom data. That table is meant to be shared across all instances. In a function I'm updating a field like so

$database = \Drupal::database();
$database->update('custom_table')->condition('id', $my_id, '=')->fields(['full_name' => $fullname, 'address' => $address])->execute();

This works on my main site. Unfortunately in the other multisite instances that's using the same function, this is causing an error. In the error I have

Base table or view not found: 1146 Table 'database.myprefix_custom_table' doesn't exist

I realize that it's trying to prepend the prefix for the table. But it's a table that every site is meant to share. I don't want a prefix to be used.

I noticed that the update method can use options as a parameter https://api.drupal.org/api/drupal/core%21lib%21Drupal%21Core%21Database%21Connection.php/function/Connection%3A%3Aupdate/8.2.x

But I'm not sure if I can tell it not to use a prefix in the options I can supply.

I understand that I can just use the query method instead of using the update method (I think) but I would like to know: Is it possible to force the update method for the connection object to not use the database prefix?

UPDATE: This was suggested as a duplicate: How to identify multi-site programmatically? But that isn't related to my problem.

In that example it's identifying what site it's on, but it's not performing anything with a database. I know how I can check what site it's on. That's not a problem. I need to call an actual database method and get rid of the prefix it's automatically applying.

In my code

$database->update('custom_table')->condition('id', $my_id, '=')->fields(['full_name' => $fullname, 'address' => $address])->execute();

I'm not even supplying the prefix. It's automatically applying it without my knowledge if it's being run on another site.

Answer 1

Looking at the comments in settings.php, you may well be able to do something like this:

$databases['default']['default'] = [
  'database' => 'db_name',
  'username' => 'root',
  'password' => 'root',
  'host' => 'localhost',
  'port' => '3306',
  'driver' => 'mysql',
  'prefix' => [
    'default' => 'shared_',
    'custom_table' => '',
  ],
];

I haven't tried it, but in theory that should set the prefix for all tables to shared_, except for the custom one, which would have no prefix.