Hi, all,
We are upgrading our application to use SA0.8.0. For reason outside our
control, some XP workstations are using old sybase ODBC driver and we
cannot upgrade them as of yet.
The sybase driver will cause this problem in the following situation:
1) we have a table that have a field of type 'bit' to hold boolean value
(i.e. 0 for false and 1 for true)
2) we need to select subset data out of this table based on this flag
When we run something like
session.query(SubProduct).filter(Product.isTradeable==True)
we get this error message:
DatabaseError: (DatabaseError) Msg 257, Level 16, State 1, Line 1
Implicit conversion from datatype 'CHAR' to 'BIT' is not allowed. Use the
CONVERT function to run this query.
Msg 257, Level 16, State 1, Line 1
Implicit conversion from datatype 'CHAR' to 'BIT' is not allowed. Use the
CONVERT function to run this query.
'SELECT SUBPRODUCT ... WHERE Product.id_tradeable = @id_tradeable_1'
{'@id_tradeable_1': '1'}
I am trying to put in place a workaround: If I can convert the sql
statement to something like so
'SELECT SUBPRODUCT ... WHERE Product.id_tradeable = *convert(bit,
@id_tradeable_1)'* {'@id_tradeable_1': '1'}
I believe I can avoid the sybase SQL exception regardless of client driver
version
So I implemented this class
import sqlalchemy.types as satypes
from sqlalchemy import func
from sqlalchemy.sql.expression import type_coerce
class SybaseBit( satypes.TypeDecorator):
impl = satypes.Boolean
def bind_expression(self, bindvalue):
# bindvalue = type_coerce(bindvalue, satypes.Integer)
return func.convert(bit, bindvalue)
It failed because 'bit' is not defined there. If I put in a string 'bit',
the generated sql is very close to what I want.
So my question is:
What is the proper way to implement this?
Cheers, Tony
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