fix relative media_file path

FileField should store a relative path, to make their "url" attribute work

tubesync/sync/migrations/0013_fix_elative_media_file.py

@@ -0,0 +1,25 @@
+# Generated by Django 3.2.12 on 2022-04-06 06:19
+
+from django.conf import settings
+from django.db import migrations, models
+
+
+def fix_media_file(apps, schema_editor):
+    Media = apps.get_model('sync', 'Media')
+    for media in Media.objects.filter(downloaded=True):
+        download_dir = str(settings.DOWNLOAD_ROOT)
+
+        if media.media_file.name.startswith(download_dir):
+            media.media_file.name = media.media_file.name[len(download_dir) + 1:]
+            media.save()
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('sync', '0012_alter_media_downloaded_format'),
+    ]
+
+    operations = [
+        migrations.RunPython(fix_media_file)
+    ]