Add unique constraint on UnitRespondingAgency

payroll/migrations/0026_unique_unitrespondingagency.py

@@ -0,0 +1,17 @@
+# Generated by Django 2.0.2 on 2019-03-04 22:25
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('payroll', '0025_rename_education_taxonomy'),
+    ]
+
+    operations = [
+        migrations.AlterUniqueTogether(
+            name='unitrespondingagency',
+            unique_together={('unit', 'reporting_year')},
+        ),
+    ]

payroll/models.py

@@ -272,6 +272,8 @@ class UnitRespondingAgency(models.Model):
     '''
     Associate units and responding agencies for a given year, so data from
     that year can be linked to a specific source file.
+
+    There should only be one responding agency per unit, per year.
     '''
     unit = models.ForeignKey(
         'Employer',
@@ -285,6 +287,9 @@ class UnitRespondingAgency(models.Model):
     )
     reporting_year = models.IntegerField()
 
+    class Meta:
+        unique_together = ('unit', 'reporting_year')
+
 
 class EmployerTaxonomy(models.Model):
     '''