fix: shifting category field from ManyToManyRel to OneToOneField

book/migrations/0007_remove_book_category_book_category.py

+# Generated by Django 5.0.7 on 2024-07-16 05:45
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('book', '0006_alter_book_category'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='book',
+            name='category',
+        ),
+        migrations.AddField(
+            model_name='book',
+            name='category',
+            field=models.OneToOneField(blank=True, null=True, on_delete=django.db.models.deletion.SET_NULL, to='book.category'),
+        ),
+    ]

book/models.py

@@ -21,7 +21,9 @@ class Book(models.Model):
     isbn = models.CharField(max_length=15, default="xxxxxxxxx-x")
     description = models.CharField(max_length=255, blank=True, null=True)
     cover_image = models.ImageField(upload_to="uploads", blank=True, null=True)
-    category = models.ManyToManyField(Category, blank=True, null=True)
+    category = models.OneToOneField(
+        Category, on_delete=models.SET_NULL, blank=True, null=True
+    )
     created_at = models.DateTimeField(auto_now_add=True)
     updated_at = models.DateTimeField(auto_now=True)