Initial

backend/common/form/img_with_preview.py

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+from django.conf import settings
+from django.core.files.uploadedfile import UploadedFile
+from django.db import models
+from django.forms import widgets
+
+from PIL import Image, ImageOps
+
+
+def makeThumnail(data: UploadedFile, size: 'tuple[int, int]'):
+    with Image.open(data) as img:
+        ImageOps.exif_transpose(img, in_place=True)
+        img.thumbnail(size)
+        if img.mode != 'RGB':
+            img = img.convert('RGB')
+        data.seek(0)
+        data.truncate()
+        img.save(data, 'jpeg')
+
+
+class ImageFileWidget(widgets.ClearableFileInput):
+    template_name = 'forms/img-with-preview.html'
+
+    def get_context(self, name, value, attrs):
+        context = super().get_context(name, value, attrs)
+        context['MEDIA_URL'] = settings.MEDIA_URL
+        return context
+
+
+class ThumbnailImageField(models.ImageField):
+    __del_image_on_save = False
+
+    def formfield(self, **kwargs):
+        kwargs['widget'] = ImageFileWidget
+        return super().formfield(**kwargs)
+
+    def save_form_data(self, instance, data):
+        if data is False:
+            self.__del_image_on_save = True
+        if isinstance(data, UploadedFile):
+            makeThumnail(data, (800, 600))  # only on create
+            # on update: django.db.models.fields.files.ImageFieldFile
+        super().save_form_data(instance, data)
+
+    def pre_save(self, model_instance, add):
+        if self.__del_image_on_save:
+            self.__del_image_on_save = False
+            self.deletePreviousImage(model_instance)
+        return super().pre_save(model_instance, add)
+
+    def deletePreviousImage(self, instance: models.Model):
+        if not instance.pk:
+            return
+        prev = instance.__class__.objects.get(pk=instance.pk)
+        imgField = getattr(prev, self.attname)
+        imgField.delete(save=False)