Add a migration

backend/api/migrations/0019_auto_20211124_0506.py

@@ -0,0 +1,30 @@
+# Generated by Django 3.2.8 on 2021-11-24 05:06
+
+from django.db import migrations, models
+import django.db.models.expressions
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0018_alter_label_background_color'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='span',
+            unique_together=set(),
+        ),
+        migrations.AddConstraint(
+            model_name='span',
+            constraint=models.CheckConstraint(check=models.Q(('start_offset__gte', 0)), name='startOffset >= 0'),
+        ),
+        migrations.AddConstraint(
+            model_name='span',
+            constraint=models.CheckConstraint(check=models.Q(('end_offset__gte', 0)), name='endOffset >= 0'),
+        ),
+        migrations.AddConstraint(
+            model_name='span',
+            constraint=models.CheckConstraint(check=models.Q(('start_offset__lt', django.db.models.expressions.F('end_offset'))), name='start < end'),
+        ),
+    ]