add unique constraint to UserExternalId (#32833)

src/authentic2/migrations/0024_auto_20190617_1113.py

@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.20 on 2019-06-17 09:13
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('custom_user', '0016_auto_20180925_1107'),
+        ('authentic2', '0023_auto_20181031_0900'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='LDAPUser',
+            fields=[
+            ],
+            options={
+                'proxy': True,
+            },
+            bases=('custom_user.user',),
+        ),
+        migrations.AlterUniqueTogether(
+            name='userexternalid',
+            unique_together=set([('source', 'external_id')]),
+        ),
+    ]

src/authentic2/models.py

@@ -75,6 +75,9 @@ class UserExternalId(models.Model):
     class Meta:
         verbose_name = _('user external id')
         verbose_name_plural = _('user external ids')
+        unique_together = [
+            ('source', 'external_id'),
+        ]
 
 
 @six.python_2_unicode_compatible