Dynamic Generation of Rules

The rule definition itself is just ruby code, which means you can use code to generate your rules¹.

rule 'Log whenever a Virtual Switch Changes' do
  items.select { |item| item.is_a? Switch }
       .select { |item| item.label&.include? 'Virtual' }
       .each do |item|
         changed item
       end

  run { |event| logger.info "#{event.item.id} changed from #{event.was} to #{event.state}" }
end

Which is the same as

virtual_switches = items.select { |item| item.is_a? Switch }
                        .select { |item| item.label&.include? 'Virtual' }

rule 'Log whenever a Virtual Switch Changes 2' do
  changed virtual_switches
  run { |event| logger.info "#{event.item.id} changed from #{event.was} to #{event.state} 2" }
end

This will accomplish the same thing, but create a new rule for each virtual switch*

virtual_switches = items.select { |item| item.is_a? Switch }
                        .select { |item| item.label&.include? 'Virtual' }

virtual_switches.each do |switch|
  rule "Log whenever a #{switch.label} Changes" do
    changed switch
    run { |event| logger.info "#{event.item.id} changed from #{event.was} to #{event.state} 2" }
  end
end

Take care when doing this as the the items/groups are processed when the rules file is processed, meaning that new items/groups will not automatically generate new rules. ↩