Ytdyklly

I have written an update method for my API.But in the end it ended up taking more than 100 lines of code.Just wanted suggestions and tips on how to shorten the code

My update method:

 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

The update method also has to delete from database by comparing the api and db fields .If user creates new object then it has to be added to database