Merge branch '16-unable-to-borrow-bookcopy' into 'master'

Resolve "Unable to borrow bookcopy"

Closes #16

See merge request AlekSIS/AlekSIS-App-Exlibris!21

aleksis/apps/exlibris/migrations/0003_add_default_value_borrow_count.py

+# Generated by Django 3.0.3 on 2020-02-05 15:55
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('exlibris', '0002_db_indexes'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='bookcopy',
+            name='borrow_count',
+            field=models.PositiveSmallIntegerField(default=0, verbose_name='Number of borrowings'),
+        ),
+    ]

aleksis/apps/exlibris/models.py

@@ -67,7 +67,7 @@ class BookCopy(models.Model):
     )
 
     borrow_count = models.PositiveSmallIntegerField(
-        verbose_name=_("Number of borrowings"), blank=True, null=True
+        verbose_name=_("Number of borrowings"), default=0
     )
     condition = models.CharField(
         verbose_name=_("Condition"), choices=CONDITION_CHOICES, max_length=1, blank=True