[GitHub] [incubator-superset] agrawaldevesh commented on a change in pull request #7131: Make timestamp expression native SQLAlchemy element

[GitBox <gi...@apache.org>]

agrawaldevesh commented on a change in pull request #7131: Make timestamp expression native SQLAlchemy element
URL: https://github.com/apache/incubator-superset/pull/7131#discussion_r277174784
 
 

 ##########
 File path: superset/db_engine_specs.py
 ##########
 @@ -83,6 +85,24 @@
 }
 
 
+class TimestampExpression(ColumnClause):
+    def __init__(self, expr: str, col: ColumnClause, **kwargs):
+        """Sqlalchemy class that can be can be used to render native column elements
+        respeting engine-specific quoting rules as part of a string-based expression.
+
+        :param expr: Sql expression with '{col}' denoting the locations where the col
+        object will be rendered.
+        :param col: the target column
+        """
+        super().__init__(expr, **kwargs)
+        self.col = col
+
+
+@compiles(TimestampExpression)
+def compile_timegrain_expression(element: TimestampExpression, compiler, **kw):
+    return element.name.replace('{col}', compiler.process(element.col, **kw))
 
 Review comment:
   What is "name" of a ColumnClause ? 
   
   Do we need to pass this further via the compiler ? Is this supposed to return a string back or is it supposed to return some sqlalchemy struct, and so we might have to do:
   
   ```
   compiler.process(element.name.replace('{col}', compiler.process(element.col, **kw)))
   ```

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