def update(self, instance, validated_data):
    levels = self.initial_data.get('levels')
    categories = self.initial_data['selectedCategories']
    instance.name = validated_data.get('name', instance.name)
    instance.description = validated_data.get('description', instance.description)
    instance.tenant = self.context['request'].user.tenant
    levels_it_has = [workflow_level.level for workflow_level in WorkflowLevel.objects.filter(workflow=instance).order_by('level') ]

    for level in levels:
        # Check if editing existing level
        if WorkflowLevel.objects.filter(workflow=instance,level=level['level']).exists():
             level_var = WorkflowLevel.objects.get(workflow=instance,level=level['level'])
             level_var.level = level['level']
             level_var.operation=level['operation']
             level_var.save()
        #If creating new Level
        else:
            level_var = WorkflowLevel()
            level_var.workflow = instance
            level_var.level = level['level']
            level_var.operation = level['operation']
            level_var.save()

        ########### Level Permissions ############3#########

        for permission in level['workflow_permissions']:
            permission_obj = WorkflowPermission.objects.get(short_name=permission['short_name'])
            permissions_in_level = [ perm.permission.short_name for perm in
                                     WorkflowLevelPermission.objects.filter(
                                        level=level_var,permission=permission_obj,
                                        level__workflow=instance).select_related('permission') ]


            if not level_permissions.exists():
                permission = WorkflowLevelPermission()
                permission.level = level_var
                permission.permission = permission_obj
                permission.save()

            new_perms=[ perm.permission.short_name for perm in
                       WorkflowLevelPermission.objects.filter(
                           level=level_var,
                           level__workflow=instance).select_related('permission') ]


    ####################### DELETE PERMISSIONS ####################################

            if len(new_perms) > len(level['workflow_permissions']):
                short_names = [perm['short_name'] for perm in level['workflow_permissions'] ]
                perm_to_delete = [item for item in new_perms if item not in short_names]
                workflow_permission_to_delete = WorkflowLevelPermission.objects.filter(level=level_var,level__workflow=instance,permission__short_name__in=perm_to_delete)
                workflow_permission_to_delete.delete()

        if len(level['workflow_permissions']) == 0:
            WorkflowLevelPermission.objects.filter(level=level_var,level__workflow=instance).delete()


    ####################### DELETE LEVELS ####################################


    if len(levels_it_has) > len(levels):
        level_numbers = [lev['level'] for lev in levels]
        level_to_delete = [item for item in levels_it_has if item not in level_numbers]
        workflow_level_to_delete = WorkflowLevel.objects.filter(workflow=instance,level__in=level_to_delete)
        workflow_level_to_delete.delete()



    ##########################################################################

    for category in categories:
        if not WorkflowCategoryLink.objects.filter(workflow=instance,target_type__short_name=category['short_name']):
            workflow_category = WorkflowCategory.objects.get(short_name=category['short_name'])
            workflow_category_link = WorkflowCategoryLink()
            workflow_category_link.workflow=instance
            workflow_category_link.target_type=workflow_category
            workflow_category_link.save()

    new_categories = [cat.target_type.short_name for cat in WorkflowCategoryLink.objects.filter(workflow=instance).select_related('target_type')]

    ######################## DELETE CATEGORIES ##############################

    if len(new_categories)> len(categories):
        short_names = [cacat['short_name'] for cat in categories]
        category_to_delete = [item for item in new_categories if item not in short_names]
        category_link_to_delete = WorkflowCategoryLink.objects.filter(workflow=instance,target_type__short_name__in=category_to_delete)
        category_link_to_delete.delete()

    instance.save()
    return instance