How to trigger a function when a custom field is edited/created in redmine - plugins

Question

I have been researching about this term for so many hours, but I found anything useful yet.
Hope you can help us building this redmine plugin, or provide us some research links to help us find the correct key.
What we want to build
The thing is we want to update one custom field in redmine (let's name it 'Target_CF') whenever another one is created or updated.
We are looking for incrementing possible values of Target_CF, so we can have all custom field's names available to select.
Of course, we want to achieve this without directly editing Redmine's Core, so we thought developing a plugin would be the best approach.
Our plugin also creates and configures a new custom field (the one mentioned above), but I will let this out of the question, because I think it is not relevant for this.
Where we are right now
We have identified some hooks that could be useful for us, as the following:
:controller_custom_fields_new_after_save
:controller_custom_fields_edit_after_save
We have the following directories/files structure so far:
plugins/
custom_plugin/
init.rb
lib/
hooks.rb
The code we have written
init.rb
require_dependency 'hooks'
Redmine::Plugin.register :custom_plugin do
name 'custom_plugin'
author 'author name'
description 'description text'
version '1.0.0'
end
hooks.rb
class Hooks < Redmine::Hook::ViewListener
def controller_custom_fields_edit_after_save(context={ })
#target_custom_field_name = "Target_CF"
CustomField.find_by_name(#target_custom_field_name).possible_values.push(context[:custom_field].name)
end
end
The result of this code is none. I mean, no erros, no updates, nothing at all. There is no change in our possible values after editing/creating another custom field. We are sure there is something we don't know, some concept or workflow, and due to this we are doing something so badly.
Please, help us understeand what we are missing.
Previously we have succesfully developed another plugin that overwrites certain views. So we have kind of little skills in views related plugins, but zero experience at all at controllers ones.
We are using a Redmine 3.2.0 stack by Bitnami and a mysql database.

Answer 1

Well, finally we found out how to extend base controller's methods. I will post it here so hopefully this can be useful to anyone who finds the same doubts we had.
After some more researching, we conclude that it is mandatory to extend base controllers, in order to not directly modify core methods.
This is our final directories/files structures:
plugins/
custom_plugin/
init.rb
lib/
custom_plugin/
issue_custom_field_patch.rb
We previously stated that we could use some hooks to inject our desired functionality, but it seems not to work that way with controllers. On the other hand, we built a patch which will extend target class functionality.
Our final working code
Init.rb
require 'redmine'
ActionDispatch::Callbacks.to_prepare do
require_dependency 'issue_custom_field'
unless IssueCustomField.included_modules.include? CustomPlugin::IssueCustomFieldPatch
IssueCustomField.send(:include, CustomPlugin::IssueCustomFieldPatch)
end
end
Redmine::Plugin.register :custom_plugin do
name 'custom_plugin'
author 'author name'
description 'description text'
version '1.0.0'
end
issue_custom_field_patch.rb
module CustomPlugin
module IssueCustomFieldPatch
def self.included(base) # :nodoc:
base.extend(ClassMethods)
base.send(:include, InstanceMethods)
base.class_eval do
unloadable
after_save :update_possible_values
end
end
end
module ClassMethods
end
module InstanceMethods
def update_possible_values
self.reload
updatedPossibleValues unless self.name == "Target_CF"
end
private
def updatedPossibleValues
#safe_attrs = ['project', 'description', 'due_date', 'category', 'status', 'assigned_to', 'priority', 'fixed_version', 'author', 'lock_version', 'created_on', 'updated_on', 'start_date', 'done_ratio', 'estimated_hours', 'is_private', 'closed_on']
#custom_fields = IssueCustomField.all.select {|cf| !cf[:position].nil?}.collect {|cf| cf.name}
#possible_values = #safe_attrs + #custom_fields
CustomField.find_by_name("Target_CF").update possible_values: #possible_values
end
end
CustomField.send(:include, IssueCustomFieldPatch)
end
Functionality explained
As we stated in the question, we needed to update Target_CF possible values each time the users create/modify/removes a custom field from Redmine.
We extended IssueCustomField's class's instance methods, triggering our new function 'updatedPossibleValues' after each save. This includes creating new custom fields, and of course, updating existing ones and removing them. Because we reload our list of possible values each time, we had to control if its position were nil. If it is, this means that custom field has been removed.
Because of the ultimate action of this patch, which is the updating of another custom field, this also triggered our function, causing an infinite loop. To prevent this, we linked our functionality to every other custom field which name was not 'Target_CF'. A bit rusty fix, but we couldn't find a better approach.
I hope this can be useful to somebody in the future, as they could invest a fraction of time that we spent on this.
Comments, fixes and improvements are very welcome.
Based on: https://www.redmine.org/projects/redmine/wiki/Plugin_Internals which is a bit outdated, but finally could complete the code with help of another resources and forums.