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",
+            ),
+        ),
+    ]

bookwyrm/models/readthrough.py

@@ -1,7 +1,8 @@
 """ progress in a book """
-from django.db import models
-from django.utils import timezone
 from django.core import validators
+from django.db import models
+from django.db.models import F, Q
+from django.utils import timezone
 
 from .base_model import BookWyrmModel
 
@@ -41,6 +42,16 @@ class ReadThrough(BookWyrmModel):
             )
         return None
 
+    class Meta:
+        """Don't let readthroughs end before they start"""
+
+        constraints = [
+            models.CheckConstraint(
+                check=Q(finish_date__gte=F("start_date")), name="chronology"
+            )
+        ]
+        ordering = ("-start_date",)
+
 
 class ProgressUpdate(BookWyrmModel):
     """Store progress through a book in the database."""