This works correctly for the author field

However it displays the same message for the modified field. That one cannot be corrected as its readonly. Just saving the article fixes that one.

This is general message, which comes from User class, anytime it cannot find a user

To me, this message should not be show up, maximum just logged. But in past someone complain "that it is right to show it up". I do not remember detail anymore :)

There were long discussions and and as long as we don't have a solution how to process deletion of users, We could only improve the message.
BTW: my opinion is: Don't allow to delete userentries, just trash and make anonymous.

@brianteeman thanks, I did not see that. So me need different messages for different cases.

@Fedik It always looks likee a bug when it is not possible to save an article. So the user must know why. It looks more as an error than a warning

So me need different messages for different cases.

yeah - thats what I am thinking

It always looks likee a bug when it is not possible to save an article.

Yeah I understood. I think it can be a message for each user field. Kind of:

<field
  name="created_by"
  type="user"
  label="COM_CONTENT_FIELD_CREATED_BY_LABEL"
  validate="UserId"
  message="A valid User ID is required, please make sure User is selected."
/>

Or globaly, throw an exception here:

if (!$db->setQuery($query)->loadResult()) {
 throw new RuntimeException('Blablabla user id is wrong');
}
return true;

Both approaches can work, but first one allow to have a specific message per form field.

A rule on the field looks good.
I ask myself why we need to check the modified_id? It is overwritten by the current users id on save and has no relevance on other places. Or am I missing something?

A rule on the field looks good.

Agreed - a nice solution that allows better error messages

I ask myself why we need to check the modified_id? It is overwritten by the current users id on save and has no relevance on other places. Or am I missing something?

It might be useful to know that the last person who modified the content is no longer an active member. But only as an information.

The rule already in that form (I copied form there), only need to add an attribute message="Blabla validation error"

I have tested this item ✅ successfully on 8b32598

Tested succcessfully in Joomla 4.3.0-rc3-dev of 4 April using PHP 8.1.16

Sorry to say that but this pr is not ready and I set it to draft. The messag is misleading if the modified_by user is deleted.

This pull request has been automatically rebased to 4.4-dev.

Closing see #41048