fix: dm get schema

Author: XiaJunjie2020

backend/apps/db/db.py

@@ -323,7 +323,7 @@ def get_schema(ds: CoreDatasource):
         if equals_ignore_case(ds.type, 'dm'):
             with dmPython.connect(user=conf.username, password=conf.password, server=conf.host,
                                   port=conf.port, **extra_config_dict) as conn, conn.cursor() as cursor:
-                cursor.execute("""select OBJECT_NAME from dba_objects where object_type='SCH'""", timeout=conf.timeout)
+                cursor.execute("""SELECT USERNAME FROM ALL_USERS""", timeout=conf.timeout)
                 res = cursor.fetchall()
                 res_list = [item[0] for item in res]
                 return res_list