Make books unique only fo one school.

biscuit/apps/exlibris/migrations/0007_book_unique_school.py

+# Generated by Django 2.2.3 on 2019-07-30 20:37
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0010_auto_20190730_2237'),
+        ('exlibris', '0006_school_book'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='book',
+            unique_together={('school', 'title', 'author', 'edition', 'year')},
+        ),
+    ]

biscuit/apps/exlibris/models.py

@@ -34,7 +34,7 @@ class Book(SchoolRelated):
         return True
 
     class Meta:
-        unique_together = [['title', 'author', 'edition', 'year']]
+        unique_together = [['school', 'title', 'author', 'edition', 'year']]
 
 
 class BookCopy(models.Model):