Read the default schema from the server with the ibm_db driver

ibm_db_sa/ibm_db.py

@@ -297,7 +297,15 @@ def create_connect_args(
     @log_entry_exit
     def _get_default_schema_name(self, connection):
         logger.debug("Fetching current schema from DB2")
-        schema = connection.connection.get_current_schema()
+        # Ask the server. ibm_db_dbi's get_current_schema() falls back to the
+        # user argument passed to connect(), which is empty when credentials
+        # are supplied in the DSN, so it can return '' for a valid session.
+        if hasattr(connection, "exec_driver_sql"):
+            result = connection.exec_driver_sql("VALUES CURRENT SCHEMA")
+        else:  # SQLAlchemy < 1.4
+            result = connection.execute("VALUES CURRENT SCHEMA")
+        schema = result.scalar()
+        schema = schema.strip() if schema else schema
         logger.debug("Current schema returned: %s", schema)
         normalized_schema_name = self.normalize_name(schema)
         logger.debug("Normalized schema: %s", normalized_schema_name)

test/test_default_schema.py

@@ -0,0 +1,63 @@
+"""Default schema detection for the ibm_db dialect."""
+
+from sqlalchemy import Column, Integer, Table, inspect
+from sqlalchemy.testing import fixtures
+from sqlalchemy.testing.assertions import eq_
+
+from ibm_db_sa.ibm_db import DB2Dialect_ibm_db
+
+
+class _Result:
+    def __init__(self, value):
+        self.value = value
+
+    def scalar(self):
+        return self.value
+
+
+class _DBAPIConnection:
+    # ibm_db_dbi returns the user passed to connect(), which is '' when the
+    # credentials are part of the DSN.
+    def get_current_schema(self):
+        return ""
+
+
+class _Connection:
+    connection = _DBAPIConnection()
+
+    def __init__(self):
+        self.statements = []
+
+    def exec_driver_sql(self, statement):
+        self.statements.append(statement)
+        return _Result("DB2INST1 ")
+
+
+class TestDefaultSchemaName(fixtures.TestBase):
+    def test_uses_server_current_schema(self):
+        connection = _Connection()
+        eq_(DB2Dialect_ibm_db()._get_default_schema_name(connection), "db2inst1")
+        eq_(connection.statements, ["VALUES CURRENT SCHEMA"])
+
+
+class TestDefaultSchemaReflection(fixtures.TestBase):
+    __only_on__ = "ibm_db_sa+ibm_db_sa"
+    __backend__ = True
+
+    def test_default_schema_matches_server(self, connection):
+        current = connection.exec_driver_sql("VALUES CURRENT SCHEMA").scalar()
+        expected = connection.dialect.normalize_name(current.strip())
+        eq_(connection.dialect.default_schema_name, expected)
+        eq_(inspect(connection).default_schema_name, expected)
+
+    def test_reflection_without_schema(self, metadata, connection):
+        Table(
+            "default_schema_reflect",
+            metadata,
+            Column("id", Integer, primary_key=True, autoincrement=False),
+            Column("amount", Integer),
+        ).create(connection)
+        inspector = inspect(connection)
+        eq_("default_schema_reflect" in inspector.get_table_names(), True)
+        columns = inspector.get_columns("default_schema_reflect")
+        eq_([c["name"] for c in columns], ["id", "amount"])