feat: add LetterImage model

backend/letters/migrations/0006_letterimage.py

@@ -0,0 +1,29 @@
+# Generated by Django 6.0.4 on 2026-04-11 20:17
+
+import uuid
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("letters", "0005_letter_encrypted_dek"),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name="LetterImage",
+            fields=[
+                ("public_id", models.UUIDField(default=uuid.uuid4, editable=False, primary_key=True, serialize=False)),
+                ("file_name", models.CharField(max_length=255)),
+                ("file", models.FileField(upload_to="encrypted-images/")),
+                (
+                    "letter",
+                    models.ForeignKey(
+                        on_delete=django.db.models.deletion.CASCADE, related_name="images", to="letters.letter"
+                    ),
+                ),
+            ],
+        ),
+    ]

backend/letters/models.py

@@ -38,3 +38,13 @@ class Letter(models.Model):
 
     def __str__(self):
         return f"{self.type} - {self.status}"
+
+
+class LetterImage(models.Model):
+    public_id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
+    letter = models.ForeignKey(Letter, on_delete=models.CASCADE, related_name="images")
+    file_name = models.CharField(max_length=255)
+    file = models.FileField(upload_to="encrypted-images/")
+
+    def __str__(self):
+        return f"Image {self.public_id} for {self.letter}"

backend/letters/tests.py

@@ -1,7 +1,10 @@
 from django.contrib.auth import get_user_model
+from django.core.files.base import ContentFile
 from django.test import TestCase
 from rest_framework.test import APITestCase
 
+from letters.models import LetterImage
+
 from .models import Letter
 
 User = get_user_model()
@@ -75,3 +78,28 @@ class LetterAPITest(APITestCase):
             response.data["non_field_errors"],
             ["encrypted_dek is required when encrypted_content and encrypted_metadata are present"],
         )
+
+
+class LetterImageModelTest(TestCase):
+    def setUp(self):
+        self.user = User.objects.create_user(email="img_test@pi-ku.app", password="password1234")
+        self.letter = Letter.objects.create(user=self.user, type="KEPT", status="DRAFT")
+
+    def test_create_letter_image(self):
+        """Test images can be associated with a letter (many to 1)"""
+        image_content = ContentFile(b"fake-encrypted-data", name="test_image.bin")
+        letter_image = LetterImage.objects.create(
+            letter=self.letter, file_name="encrypted_image.enc", file=image_content
+        )
+        self.assertEqual(letter_image.letter, self.letter)
+        self.assertTrue(letter_image.file.name.startswith("encrypted-images/"))
+        self.assertIsNotNone(letter_image.public_id)
+
+    def test_letter_cascade_deletes_images(self):
+        """TTest when a letter is deleted, its encrypted images are also removed"""
+        LetterImage.objects.create(
+            letter=self.letter, file_name="will_be_deleted.jpg", file=ContentFile(b"data", name="del.bin")
+        )
+        self.assertEqual(LetterImage.objects.count(), 1)
+        self.letter.delete()
+        self.assertEqual(LetterImage.objects.count(), 0)