What's the problem?
===================
TL;DR: When the user enters an incorrect default value, its
corresponding param-input will disappear
When creating a parameter from SQL, we perform cast_to_ruby, which means
that if the default value given by the user is invalid, the entire
parameter will not be added to the param_list of the query.
This behavior is very confusing, and users will not understand why an
incorrect initial value will cause the param-input to disappear.
What's the fix?
================
The cast_to_ruby process is canceled in create_from_sql, so that
param-input with incorrect default value will still be displayed.
We have a simple validation process on the front end, which is enough to
prompt whether some default inputs are incorrect.
We used `with_deleted` incorrectly in the code. This method does not exist
on `User`, `Badge`, and `Group`. This will cause an error when entering a
numeric id in these three parameter input, forcing the user to enter the
name/username of these inputs.
See https://github.com/discourse/discourse-data-explorer/pull/307#issuecomment-2291017256
This commit updates the plugin to the latest guidelines, as shown in
discourse-plugin-skeleton, which involves moving a lot of the code to
dedicated files, use proper namespaces, use the autoloader as much as
possible, etc.