refactor(db_api): cleanup the code (#636)

Author: Ilya Gurov

google/cloud/spanner_dbapi/_helpers.py

@@ -19,23 +19,16 @@
 
 
 SQL_LIST_TABLES = """
-            SELECT
-              t.table_name
-            FROM
-              information_schema.tables AS t
-            WHERE
-              t.table_catalog = '' and t.table_schema = ''
-            """
-
-SQL_GET_TABLE_COLUMN_SCHEMA = """SELECT
-                COLUMN_NAME, IS_NULLABLE, SPANNER_TYPE
-            FROM
-                INFORMATION_SCHEMA.COLUMNS
-            WHERE
-                TABLE_SCHEMA = ''
-            AND
-                TABLE_NAME = @table_name
-            """
+SELECT table_name
+FROM information_schema.tables
+WHERE table_catalog = '' AND table_schema = ''
+"""
+
+SQL_GET_TABLE_COLUMN_SCHEMA = """
+SELECT COLUMN_NAME, IS_NULLABLE, SPANNER_TYPE
+FROM INFORMATION_SCHEMA.COLUMNS
+WHERE TABLE_SCHEMA = '' AND TABLE_NAME = @table_name
+"""
 
 # This table maps spanner_types to Spanner's data type sizes as per
 #   https://cloud.google.com/spanner/docs/data-types#allowable-types
@@ -64,10 +57,9 @@ def _execute_insert_heterogenous(transaction, sql_params_list):
 
 def _execute_insert_homogenous(transaction, parts):
     # Perform an insert in one shot.
-    table = parts.get("table")
-    columns = parts.get("columns")
-    values = parts.get("values")
-    return transaction.insert(table, columns, values)
+    return transaction.insert(
+        parts.get("table"), parts.get("columns"), parts.get("values")
+    )
 
 
 def handle_insert(connection, sql, params):

google/cloud/spanner_dbapi/connection.py

@@ -40,6 +40,23 @@
 MAX_INTERNAL_RETRIES = 50
 
 
+def check_not_closed(function):
+    """`Connection` class methods decorator.
+
+    Raise an exception if the connection is closed.
+
+    :raises: :class:`InterfaceError` if the connection is closed.
+    """
+
+    def wrapper(connection, *args, **kwargs):
+        if connection.is_closed:
+            raise InterfaceError("Connection is already closed")
+
+        return function(connection, *args, **kwargs)
+
+    return wrapper
+
+
 class Connection:
     """Representation of a DB-API connection to a Cloud Spanner database.
 
@@ -328,15 +345,6 @@ def snapshot_checkout(self):
 
             return self._snapshot
 
-    def _raise_if_closed(self):
-        """Helper to check the connection state before running a query.
-        Raises an exception if this connection is closed.
-
-        :raises: :class:`InterfaceError`: if this connection is closed.
-        """
-        if self.is_closed:
-            raise InterfaceError("connection is already closed")
-
     def close(self):
         """Closes this connection.
 
@@ -391,15 +399,13 @@ def rollback(self):
             self._release_session()
             self._statements = []
 
+    @check_not_closed
     def cursor(self):
-        """Factory to create a DB-API Cursor."""
-        self._raise_if_closed()
-
+        """Factory to create a DB API Cursor."""
         return Cursor(self)
 
+    @check_not_closed
     def run_prior_DDL_statements(self):
-        self._raise_if_closed()
-
         if self._ddl_statements:
             ddl_statements = self._ddl_statements
             self._ddl_statements = []
@@ -454,6 +460,7 @@ def run_statement(self, statement, retried=False):
             ResultsChecksum() if retried else statement.checksum,
         )
 
+    @check_not_closed
     def validate(self):
         """
         Execute a minimal request to check if the connection
@@ -468,8 +475,6 @@ def validate(self):
         :raises: :class:`google.cloud.exceptions.NotFound`: if the linked instance
                   or database doesn't exist.
         """
-        self._raise_if_closed()
-
         with self.database.snapshot() as snapshot:
             result = list(snapshot.execute_sql("SELECT 1"))
             if result != [[1]]: