update area model to be unique on gss and area type

hub/migrations/0055_change_gss_uniqueness.py

@@ -0,0 +1,22 @@
+# Generated by Django 4.2.5 on 2023-11-07 15:45
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("hub", "0054_fill_datatype_area_type"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="area",
+            name="gss",
+            field=models.CharField(max_length=30),
+        ),
+        migrations.AlterUniqueTogether(
+            name="area",
+            unique_together={("gss", "area_type")},
+        ),
+    ]

hub/models.py

@@ -497,7 +497,7 @@ class Meta:
 
 class Area(models.Model):
     mapit_id = models.CharField(max_length=30)
-    gss = models.CharField(unique=True, max_length=30)
+    gss = models.CharField(max_length=30)
     name = models.CharField(max_length=200)
     area_type = models.ForeignKey(AreaType, on_delete=models.CASCADE)
     geometry = models.TextField(blank=True, null=True)
@@ -541,6 +541,9 @@ def get_by_name(cls, name, area_type="WMC"):
 
         return area
 
+    class Meta:
+        unique_together = ["gss", "area_type"]
+
 
 class AreaData(CommonData):
     area = models.ForeignKey(Area, on_delete=models.CASCADE)