`from_picture_field` and `to_picture_field` iterate over all objects

[jmsmkn]

In

django-pictures/pictures/migrations.py

Lines 58 to 74 in 721cd80

	def from_picture_field(self, from_model: type[models.Model]):
	for obj in from_model._default_manager.all().iterator():
	field_file = getattr(obj, self.name)
	field_file.delete_all()
	def to_picture_field(
	self, from_model: type[models.Model], to_model: type[models.Model]
	):
	from_field = from_model._meta.get_field(self.name)
	if hasattr(from_field.attr_class, "delete_variations"):
	# remove obsolete django-stdimage variations
	for obj in from_model._default_manager.all().iterator():
	field_file = getattr(obj, self.name)
	field_file.delete_variations()
	for obj in to_model._default_manager.all().iterator():
	field_file = getattr(obj, self.name)
	field_file.save_all()

all objects are iterated over. Similar to #120 empty objects shouldn't be considered. Suggestion:

    def from_picture_field(self, from_model: type[models.Model]):
        for obj in from_model._default_manager.exclude(
            Q(**{self.name: ""}) | Q(**{self.name: None})
        ).iterator():
            field_file = getattr(obj, self.name)
            field_file.delete_all()

    def to_picture_field(
        self, from_model: type[models.Model], to_model: type[models.Model]
    ):
        from_field = from_model._meta.get_field(self.name)
        if hasattr(from_field.attr_class, "delete_variations"):
            # remove obsolete django-stdimage variations
            for obj in from_model._default_manager.exclude(
            Q(**{self.name: ""}) | Q(**{self.name: None})
        ).iterator():
                field_file = getattr(obj, self.name)
                field_file.delete_variations()
        for obj in to_model._default_manager.exclude(
            Q(**{self.name: ""}) | Q(**{self.name: None})
        ).iterator():
            field_file = getattr(obj, self.name)
            field_file.save_all()

This results in a considerable speedup with many objects with optional picture fields when migrating from/to Django Pictures.

[codingjoe]

Hi @jmsmkn,

Thanks for reaching out and contributing such an excellent idea. Since we are doing file operations, sadly, looping is needed. But skipping objects that we don't need to process is a wonderful idea!

Would you care to submit a PR yourself? I will review and release it ASAP 👍
If not, I can also contribute it myself, but it'll probably take a little longer.

Cheerio,
Joe

[jmsmkn]

No problem, it is not urgent for me as I implemented it locally and our migration is complete now. I will make a PR when I can, hopefully end of this week.