Fixed #24742 -- Made runserver.check_migrations ignore read-only databases

Thanks Luis Del Giudice for the report, and Aymeric Augustin and Markus
Holtermann for the reviews.

2 files changed, 13 insertions, 2 deletions

diff --git a/django/db/migrations/exceptions.py b/django/db/migrations/exceptions.py
index d8b386e1ac..8b60a035fe 100644
--- a/django/db/migrations/exceptions.py
+++ b/django/db/migrations/exceptions.py
@@ -1,5 +1,6 @@
 from __future__ import unicode_literals
 
+from django.db.utils import DatabaseError
 from django.utils.encoding import python_2_unicode_compatible
 
 
@@ -53,3 +54,7 @@ class NodeNotFoundError(LookupError):
 
     def __repr__(self):
         return "NodeNotFoundError(%r)" % self.node
+
+
+class MigrationSchemaMissing(DatabaseError):
+    pass
diff --git a/django/db/migrations/recorder.py b/django/db/migrations/recorder.py
index d1071cecb7..2dcbe6c042 100644
--- a/django/db/migrations/recorder.py
+++ b/django/db/migrations/recorder.py
@@ -2,9 +2,12 @@ from __future__ import unicode_literals
 
 from django.apps.registry import Apps
 from django.db import models
+from django.db.utils import DatabaseError
 from django.utils.encoding import python_2_unicode_compatible
 from django.utils.timezone import now
 
+from .exceptions import MigrationSchemaMissing
+
 
 class MigrationRecorder(object):
     """
@@ -49,8 +52,11 @@ class MigrationRecorder(object):
         if self.Migration._meta.db_table in self.connection.introspection.table_names(self.connection.cursor()):
             return
         # Make the table
-        with self.connection.schema_editor() as editor:
-            editor.create_model(self.Migration)
+        try:
+            with self.connection.schema_editor() as editor:
+                editor.create_model(self.Migration)
+        except DatabaseError as exc:
+            raise MigrationSchemaMissing("Unable to create the django_migrations table (%s)" % exc)
 
     def applied_migrations(self):
         """