Merge pull request #14519 from edx/nedbat/idempotent-email-uniqueness-constraint

An idempotent migration to add an email uniqueness constraint

cms/envs/common.py

@@ -959,6 +959,9 @@ INSTALLED_APPS = (
 
     # management of user-triggered async tasks (course import/export, etc.)
     'user_tasks',
+
+    # Unusual migrations
+    'database_fixups',
 )
 
 

common/djangoapps/database_fixups/__init__.py

+"""
+This app exists solely to host unusual database migrations.
+"""

common/djangoapps/database_fixups/migrations/0001_initial.py

+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+# We used to have a uniqueness constraint on auth_user.email:
+# https://github.com/edx/edx-platform/commit/c52727b0e0fb241d8211900975d3b69fe5a1bd57
+#
+# That constraint was lost in the upgrade from Django 1.4->1.8.  This migration
+# adds it back.  But because it might already exist in databases created
+# long-enough ago, we have to do it idempotently.  So we check for the
+# existence of the constraint before creating it.
+
+def add_email_uniqueness_constraint(apps, schema_editor):
+    # Do we already have an email uniqueness constraint?
+    cursor = schema_editor.connection.cursor()
+    constraints = schema_editor.connection.introspection.get_constraints(cursor, "auth_user")
+    email_constraint = constraints.get("email", {})
+    if email_constraint.get("columns") == ["email"] and email_constraint.get("unique") == True:
+        # We already have the constraint, we're done.
+        return
+
+    # We don't have the constraint, make it.
+    schema_editor.execute("create unique index email on auth_user (email)")
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+    ]
+
+    operations = [
+        migrations.RunPython(add_email_uniqueness_constraint)
+    ]

common/djangoapps/student/migrations/0010_auto_20170207_0458.py

@@ -26,9 +26,5 @@ class Migration(migrations.Migration):
     # )
 
     operations = [
-        migrations.RunSQL(
-            # Do nothing:
-            "select 1",
-            "select 1"
-        )
+        # Nothing to do.
     ]

lms/envs/common.py

@@ -2164,6 +2164,9 @@ INSTALLED_APPS = (
 
     # Ability to detect and special-case crawler behavior
     'openedx.core.djangoapps.crawlers',
+
+    # Unusual migrations
+    'database_fixups',
 )
 
 # Migrations which are not in the standard module "migrations"

openedx/core/lib/django_courseware_routers.py

@@ -51,7 +51,7 @@ class StudentModuleHistoryExtendedRouter(object):
         """
         if model_name is not None:
             model = hints.get('model')
-            if self._is_csmh(model):
+            if model is not None and self._is_csmh(model):
                 return db == self.DATABASE_NAME
         if db == self.DATABASE_NAME:
             return False