Module development and code questions

I have a requirement to have lots of fields almost 20 in a User entity. How do we get all the fields in single table so that all the fields are in a single table instead of default - field per table? I want to avoid lot of tabe joins. 

Can anyone point me in the right direction to change the displayed text in an entity reference field after I have selected from the auto complete, I ve managed to change what is displayed in the auto complete, now I want to add that change to the actual entity reference field, looking for a tutorial or guidance to learn from

Thanks

Hey,

I want to do a custom validation for a field in some of my webforms.
I came across this code:
https://www.drupal.org/docs/8/modules/webform/webform-cookbook/how-to-add-custom-validation-to-a-webform-element

this is the data from the webform devel
the field I want to do the validate on id calle `idno` 

I don't understand:
1.what are the values:
 

HI

I am using the following code to change the autocomplete text displayed in the results returned from an entity reference

$entity_type_id returns node, how would I return the content type please (e.g. Classes) I ve read loads but can't find what I am looking for.

Thanks

protected function getLabel($entity_id, $entity_type_id, $label) {

$entity = \Drupal::entityTypeManager()->getStorage($entity_type_id)->load($entity_id);

Hi,

My hoster told me to send only 300 mail by hours for avoiding spam.

So I decided to create cron job, and the cron will start every hours.

So I need to tell to the cron :

On each run only process 300 items from "email_processor". How Can I do that ?

here is my function to create mail item :

How can I run Drupal 8 batch process in Drupal form triggered by ajax submit button?

Thanks