sqlalchemy postgresql poor man's custom types

casttojson.py

# I had a fancy custom type in PG, and wanted to use it in
# SQLAlchemy. I didn't care to jump through all of the custom
# type stuff, and the type had an reasonable representation
# to JSON, and PG could convert it to/from JSON very easily.
# So I added cast conversions to PG, and then this special
# type:
class CastToJSONB(sqlalchemy.types.TypeDecorator):
    '''A JSON object where we force PostgreSQL to cast our                      
    interactions with the value to JSON. Useful when we've                     
    got a PG data type that is a pain in the ass, but has an                    
    acceptable JSON representation, and appropriate CAST functions              
    installed into the PG database.                                             
    '''  
    impl = sqlalchemy.types.JSON
    def column_expression(self, col):
        return cast(col, JSON)
    def bind_expression(self, bindparam):
        return cast(bindparam, JSON)