Made MigrationRecorder cache has_table() result if django_migrations table exists.

2 files changed, 19 insertions, 1 deletions

diff --git a/django/db/migrations/recorder.py b/django/db/migrations/recorder.py
index 50876a9ee3..cf0bd4a2ce 100644
--- a/django/db/migrations/recorder.py
+++ b/django/db/migrations/recorder.py
@@ -47,6 +47,7 @@ class MigrationRecorder:
 
     def __init__(self, connection):
         self.connection = connection
+        self._has_table = False
 
     @property
     def migration_qs(self):
@@ -54,9 +55,16 @@ class MigrationRecorder:
 
     def has_table(self):
         """Return True if the django_migrations table exists."""
+        # If the migrations table has already been confirmed to exist, don't
+        # recheck it's existence.
+        if self._has_table:
+            return True
+        # It hasn't been confirmed to exist, recheck.
         with self.connection.cursor() as cursor:
             tables = self.connection.introspection.table_names(cursor)
-        return self.Migration._meta.db_table in tables
+
+        self._has_table = self.Migration._meta.db_table in tables
+        return self._has_table
 
     def ensure_schema(self):
         """Ensure the table exists and has the correct schema."""
diff --git a/tests/migrations/test_loader.py b/tests/migrations/test_loader.py
index 800d715bc9..24e1e98c19 100644
--- a/tests/migrations/test_loader.py
+++ b/tests/migrations/test_loader.py
@@ -48,6 +48,16 @@ class RecorderTests(TestCase):
             set(),
         )
 
+    def test_has_table_cached(self):
+        """
+        The has_table() method caches a positive result and not continually
+        query for the existence of the migrations table.
+        """
+        recorder = MigrationRecorder(connection)
+        with self.assertNumQueries(1):
+            self.assertEqual(recorder.has_table(), True)
+            self.assertEqual(recorder.has_table(), True)
+
 
 class LoaderTests(TestCase):
     """