Adds database constraint for readthrough dates

bookwyrm/migrations/0083_auto_20210811_1817.py

@@ -0,0 +1,27 @@
+# Generated by Django 3.2.4 on 2021-08-11 18:17
+
+from django.db import migrations, models
+import django.db.models.expressions
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookwyrm", "0082_auto_20210806_2324"),
+    ]
+
+    operations = [
+        migrations.AlterModelOptions(
+            name="readthrough",
+            options={"ordering": ("-start_date",)},
+        ),
+        migrations.AddConstraint(
+            model_name="readthrough",
+            constraint=models.CheckConstraint(
+                check=models.Q(
+                    ("finish_date__gte", django.db.models.expressions.F("start_date"))
+                ),
+                name="chronology",
+            ),
+        ),
+    ]