Fixed #24560 -- Added a --dry-run mode to the createcachetable command.

5 files changed, 40 insertions, 4 deletions

diff --git a/django/core/management/commands/createcachetable.py b/django/core/management/commands/createcachetable.py
index 4c014c88fd..c1ec4539b6 100644
--- a/django/core/management/commands/createcachetable.py
+++ b/django/core/management/commands/createcachetable.py
@@ -22,21 +22,25 @@ class Command(BaseCommand):
             default=DEFAULT_DB_ALIAS,
             help='Nominates a database onto which the cache tables will be '
             'installed. Defaults to the "default" database.')
+        parser.add_argument('--dry-run', action='store_true', dest='dry_run',
+            help='Does not create the table, just prints the SQL that would '
+            'be run.')
 
     def handle(self, *tablenames, **options):
         db = options.get('database')
         self.verbosity = int(options.get('verbosity'))
+        dry_run = options.get('dry_run')
         if len(tablenames):
             # Legacy behavior, tablename specified as argument
             for tablename in tablenames:
-                self.create_table(db, tablename)
+                self.create_table(db, tablename, dry_run)
         else:
             for cache_alias in settings.CACHES:
                 cache = caches[cache_alias]
                 if isinstance(cache, BaseDatabaseCache):
-                    self.create_table(db, cache._table)
+                    self.create_table(db, cache._table, dry_run)
 
-    def create_table(self, database, tablename):
+    def create_table(self, database, tablename, dry_run):
         cache = BaseDatabaseCache(tablename, {})
         if not router.allow_migrate_model(database, cache.cache_model_class):
             return
@@ -74,11 +78,19 @@ class Command(BaseCommand):
             full_statement.append('    %s%s' % (line, ',' if i < len(table_output) - 1 else ''))
         full_statement.append(');')
 
+        full_statement = "\n".join(full_statement)
+
+        if dry_run:
+            self.stdout.write(full_statement)
+            for statement in index_output:
+                self.stdout.write(statement)
+            return
+
         with transaction.atomic(using=database,
                                 savepoint=connection.features.can_rollback_ddl):
             with connection.cursor() as curs:
                 try:
-                    curs.execute("\n".join(full_statement))
+                    curs.execute(full_statement)
                 except DatabaseError as e:
                     raise CommandError(
                         "Cache table '%s' could not be created.\nThe error was: %s." %
diff --git a/docs/ref/django-admin.txt b/docs/ref/django-admin.txt
index 3515c615e7..2b68f6575d 100644
--- a/docs/ref/django-admin.txt
+++ b/docs/ref/django-admin.txt
@@ -189,6 +189,13 @@ The :djadminopt:`--database` option can be used to specify the database
 onto which the cache table will be installed, but since this information is
 pulled from your settings by default, it's typically not needed.
 
+The :djadminopt:`--dry-run` option will print the SQL that would be run without
+actually running it, so you can customize it or use the migrations framework.
+
+.. versionchanged:: 1.9
+
+    The ``--dry-run`` option was added.
+
 dbshell
 -------
 
diff --git a/docs/releases/1.9.txt b/docs/releases/1.9.txt
index cd124bf602..d89354ea6a 100644
--- a/docs/releases/1.9.txt
+++ b/docs/releases/1.9.txt
@@ -166,6 +166,9 @@ Management Commands
 
 * The :djadmin:`dumpdata` command output is now deterministically ordered.
 
+* The :djadmin:`createcachetable` command now has a ``--dry-run`` flag to
+  print out the SQL rather than execute it.
+
 Models
 ^^^^^^
 
diff --git a/docs/topics/cache.txt b/docs/topics/cache.txt
index ec973a5008..1a21eab164 100644
--- a/docs/topics/cache.txt
+++ b/docs/topics/cache.txt
@@ -206,6 +206,9 @@ If you are using multiple databases, :djadmin:`createcachetable` observes the
 Like :djadmin:`migrate`, :djadmin:`createcachetable` won't touch an existing
 table. It will only create missing tables.
 
+To print the SQL that would be run, rather than run it, use the
+:djadminopt:`--dry-run` option.
+
 Multiple databases
 ~~~~~~~~~~~~~~~~~~
 
diff --git a/tests/cache/tests.py b/tests/cache/tests.py
index ffbed67197..9d29239cf6 100644
--- a/tests/cache/tests.py
+++ b/tests/cache/tests.py
@@ -943,6 +943,17 @@ class DBCacheTests(BaseCacheTests, TransactionTestCase):
         self.assertEqual(out.getvalue(),
             "Cache table 'test cache table' already exists.\n" * len(settings.CACHES))
 
+    @override_settings(CACHES=caches_setting_for_tests(
+        BACKEND='django.core.cache.backends.db.DatabaseCache',
+        # Use another table name to avoid the 'table already exists' message.
+        LOCATION='createcachetable_dry_run_mode'
+    ))
+    def test_createcachetable_dry_run_mode(self):
+        out = six.StringIO()
+        management.call_command('createcachetable', dry_run=True, stdout=out)
+        output = out.getvalue()
+        self.assertTrue(output.startswith("CREATE TABLE"))
+
     def test_createcachetable_with_table_argument(self):
         """
         Delete and recreate cache table with legacy behavior (explicitly