Implement variables_attributes create/update cases

app/services/ci/create_pipeline_schedule_service.rb

 module Ci
   class CreatePipelineScheduleService < BaseService
     def execute
-      project.pipeline_schedules.create(pipeline_schedule_params)
+      pipeline_schedule = project.pipeline_schedules.build(pipeline_schedule_params)
+
+      if variable_keys_duplicated?
+        pipeline_schedule.errors.add('variables.key', "keys are duplicated")
+
+        return pipeline_schedule
+      end
+
+      pipeline_schedule.save
+      pipeline_schedule
+    end
+
+    def update(pipeline_schedule)
+      if variable_keys_duplicated?
+        pipeline_schedule.errors.add('variables.key', "keys are duplicated")
+
+        return false
+      end
+
+      pipeline_schedule.update(pipeline_schedule_params)
     end
 
     private
 
     def pipeline_schedule_params
-      params.merge(owner: current_user)
+      @pipeline_schedule_params ||= params.merge(owner: current_user)
+    end
+
+    def variable_keys_duplicated?
+      attributes = pipeline_schedule_params['variables_attributes']
+      return false unless attributes.is_a?(Array)
+
+      attributes.map { |v| v['key'] }.uniq.length != attributes.length
     end
   end
 end