Exclude empty objects during picture migration (#120)

pictures/migrations.py

@@ -2,6 +2,7 @@
 
 from django.db import models
 from django.db.migrations import AlterField
+from django.db.models import Q
 
 from pictures.models import PictureField, PictureFieldFile
 
@@ -46,7 +47,9 @@ def alter_picture_field(
             self.update_pictures(from_field, to_model)
 
     def update_pictures(self, from_field: PictureField, to_model: Type[models.Model]):
-        for obj in to_model._default_manager.all().iterator():
+        for obj in to_model._default_manager.exclude(
+            Q(**{self.name: ""}) | Q(**{self.name: None})
+        ).iterator():
             field_file = getattr(obj, self.name)
             field_file.update_all(
                 from_aspect_ratios=PictureFieldFile.get_picture_files(

tests/test_migrations.py

@@ -144,6 +144,29 @@ class Meta:
         )
         assert path.exists()
 
+    @pytest.mark.django_db
+    def test_update_pictures__without_picture(self, request, stub_worker):
+        class ToModel(models.Model):
+            name = models.CharField(max_length=100)
+            picture = PictureField(
+                upload_to="testapp/profile/", aspect_ratios=[None, "21/9"], blank=True
+            )
+
+            class Meta:
+                app_label = request.node.name
+                db_table = "testapp_profile"
+
+        luke = Profile.objects.create(name="Luke")
+        stub_worker.join()
+        migration = migrations.AlterPictureField("profile", "picture", PictureField())
+        from_field = Profile._meta.get_field("picture")
+
+        migration.update_pictures(from_field, ToModel)
+        stub_worker.join()
+        luke.refresh_from_db()
+
+        assert not luke.picture
+
     @pytest.mark.django_db
     def test_from_picture_field(self, stub_worker, image_upload_file):
         luke = Profile.objects.create(name="Luke", picture=image_upload_file)