Fixing replica query when cluster is default

CHANGELOG.md

@@ -1,4 +1,5 @@
 ### 1.5.0
+- fix: #139: Fix to replicas query when using default as cluster name
 - feat: #133: Fix simultaneous queries error when iteration is interrupted
 - feat: #130: Add `distributed_migrations` database setting to support distributed migration queries.
 - feat: #129: Add `toYearWeek` datetime functionality

clickhouse_backend/patch/migrations.py

@@ -44,13 +44,20 @@ def _check_replicas(connection):
         return connection.has_replicas
 
     with connection.cursor() as cursor:
-        cursor.execute(
-            f"select replica_num from system.clusters where cluster={connection.migration_cluster}"
-        )
-        (replica_count,) = cursor.fetchone()
+        replica_count = _get_replicas(connection.migration_cluster, cursor)
     return replica_count >= 1
 
 
+def _get_replicas(cluster_name, cursor):
+    cursor.execute(
+        "select replica_num from system.clusters where cluster=%s", [cluster_name]
+    )
+    res = cursor.fetchone()
+    if not res:
+        return 0
+    return res[0]
+
+
 def patch_migrations():
     patch_migration_recorder()
     patch_migration()

tests/migrations/test_loader.py

@@ -15,6 +15,7 @@
 
 from clickhouse_backend import compat
 from clickhouse_backend.backend.base import DatabaseWrapper
+from clickhouse_backend.patch.migrations import _check_replicas, _get_replicas
 
 from .test_base import MigrationTestBase
 
@@ -201,6 +202,28 @@ def test_apply_unapply_distributed(self):
             conn = connections[db]
             self.assertMigrationExists(conn, "0432_ponies", "myapp", deleted=True)
 
+    def test_checking_cluster_replicas(self):
+        """
+        Tests checking cluster replicas for migrations
+        """
+        db = DatabaseWrapper(deepcopy(self.lb), alias="load_balancer")
+        connections["load_balancer"] = db
+
+        for db in self.databases:
+            wrapper = connections[db]
+            conn = wrapper.client.connection
+            has_clusters = _check_replicas(conn)
+            self.assertEqual(has_clusters, True)
+
+        with connections["default"].cursor() as cursor:
+            # testing "default" cluster name on query
+            replicas = _get_replicas("default", cursor)
+            self.assertFalse(replicas)
+
+            # testing migration_cluster query
+            replicas = _get_replicas(self.lb["OPTIONS"]["migration_cluster"], cursor)
+            self.assertEqual(replicas, 1)
+
 
 class LoaderTests(TestCase):
     """