fix: unify global config singleton and fix conn() persistence

- instance._global_config now reuses settings.config instead of creating
  a duplicate Config object. This ensures dj.config["safemode"] = False
  actually affects self.connection._config["safemode"] reads.
- schemas.py now uses _get_singleton_connection() from instance.py
  instead of the old conn() from connection.py, eliminating the
  duplicate singleton connection holder.
- dj.conn() now only creates a new connection when the singleton doesn't
  exist or reset=True (not on every call with credentials).
- test_uppercase_schema: use prompt=False for drop() calls.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/__init__.py

@@ -135,8 +135,12 @@ def conn(
 
     _check_thread_safe()
 
-    # If credentials provided or reset requested, (re)create the singleton
-    if host is not None or user is not None or password is not None or reset:
+    # If reset requested, always recreate
+    # If credentials provided and no singleton exists, create one
+    # If credentials provided and singleton exists, return existing singleton
+    if reset or (
+        instance_module._singleton_connection is None and (host is not None or user is not None or password is not None)
+    ):
         # Use provided values or fall back to config
         host = host if host is not None else _global_config.database.host
         user = user if user is not None else _global_config.database.user

src/datajoint/instance.py

@@ -12,7 +12,7 @@
 
 from .connection import Connection
 from .errors import ThreadSafetyError
-from .settings import Config, _create_config
+from .settings import Config, _create_config, config as _settings_config
 
 if TYPE_CHECKING:
     from .schemas import Schema as SchemaClass
@@ -179,7 +179,8 @@ def __repr__(self) -> str:
 # The global config is created at module load time and can be modified
 # The singleton connection is created lazily when conn() or Schema() is called
 
-_global_config: Config = _create_config()
+# Reuse the config created in settings.py — there must be exactly one global config
+_global_config: Config = _settings_config
 _singleton_connection: Connection | None = None
 
 

src/datajoint/schemas.py

@@ -16,8 +16,8 @@
 import warnings
 from typing import TYPE_CHECKING, Any
 
-from .connection import conn
 from .errors import AccessError, DataJointError
+from .instance import _get_singleton_connection
 
 if TYPE_CHECKING:
     from .connection import Connection
@@ -173,7 +173,7 @@ def activate(
         if connection is not None:
             self.connection = connection
         if self.connection is None:
-            self.connection = conn()
+            self.connection = _get_singleton_connection()
         self.database = schema_name
         if create_schema is not None:
             self.create_schema = create_schema
@@ -860,7 +860,7 @@ def list_schemas(connection: Connection | None = None) -> list[str]:
     """
     return [
         r[0]
-        for r in (connection or conn()).query(
+        for r in (connection or _get_singleton_connection()).query(
             'SELECT schema_name FROM information_schema.schemata WHERE schema_name <> "information_schema"'
         )
     ]

tests/integration/test_schema.py

@@ -265,5 +265,5 @@ class Recording(dj.Manual):
         id: smallint
         """
 
-    schema2.drop()
-    schema1.drop()
+    schema2.drop(prompt=False)
+    schema1.drop(prompt=False)