PgDB.select: add support for orderby clause specify by tuple

mylib/pgsql.py

@@ -50,6 +50,19 @@ class PgDBUnsupportedWHEREClauses(PgDBException, TypeError):
         )
 
 
+class PgDBInvalidOrderByClause(PgDBException, TypeError):
+    """
+    Raised when trying to select on table with invalid
+    ORDER BY clause provided
+    """
+
+    def __init__(self, order_by):
+        super().__init__(
+            "Invalid ORDER BY clause: {order_by}. Must be a string or a list of two values (ordering field name and direction)",
+            order_by=order_by
+        )
+
+
 class PgDB:
     """ PostgreSQL client """
 
@@ -367,7 +380,17 @@ class PgDB:
             return False
 
         if order_by:
-            sql += ' ORDER BY {0}'.format(order_by)
+            if isinstance(order_by, str):
+                sql += ' ORDER BY {0}'.format(order_by)
+            elif (
+                isinstance(order_by, (list, tuple)) and len(order_by) == 2 and
+                isinstance(order_by[0], str) and
+                isinstance(order_by[1], str) and
+                order_by[1].upper() in ('ASC', 'UPPER')
+            ):
+                sql += ' ORDER BY "{0}" {1}'.format(order_by[0], order_by[1].upper())
+            else:
+                raise PgDBInvalidOrderByClause(order_by)
 
         if just_try:
             log.debug("Just-try mode: execute SELECT query : %s", sql)