SQLAlchemy custom boolean - oracle

Question

I have an Oracle database with boolean logic implemented this way:
MYCOL NUMBER(1,0)
0 = False
-1 or 1 = True
NULL = None
With a default SQLAlchemy boolean column, -1 table value doesn't match False or True.
Is it possible to create an SQLAlchemy custom type that maps such a column to a bool python attribute?
The difficulty relies in having multiple values associated with true.
Ex:
session.query(User).filter_by(active=True)
Should generate one of these queries:
select * from user where active != 0;
select * from user where active in (-1, 1);
select * from user where 1 = (CASE WHEN active != 0 THEN 1 ELSE active end);

Answer 1

This implementation seems to work for basic queries.
Case when expression seems to be the easiest solution because operator logic isn't altered.
class CustomBoolean(sqlalchemy.types.TypeDecorator):
"""0 = False
-1 or 1 = True
NULL = None
By default, SQLAlchemy only supports 0 and 1"""
impl = Boolean
cache_ok = True
# In select or group by clause, replace col with expression: (CASE WHEN col != 0 THEN 1 ELSE col end)
def column_expression(self, col):
expr = col.expr
if isinstance(expr.type, CustomBoolean):
res = sqlalchemy.case(
(type_coerce(expr, Integer()) != sqlalchemy.literal_column("0", type_=Integer), sqlalchemy.literal_column("1", type_=Integer)),
else_=type_coerce(expr, Integer())
)
return type_coerce(res, Boolean())
expr.type = Boolean()
return expr
# In where clause, replace col with expression: (CASE WHEN col != 0 THEN 1 ELSE col end)
class comparator_factory(Boolean.Comparator):
def operate(self, op, other, **kwargs):
op1 = self
if hasattr(op1, "__clause_element__"):
clause = op1.__clause_element__()
if isinstance(clause.type, CustomBoolean):
op1 = self.normalise(clause)
op2 = other
if hasattr(op2, "__clause_element__"):
clause = op2.__clause_element__()
if isinstance(clause.type, CustomBoolean):
op2 = self.normalise(clause)
return op(
op1, op2, **kwargs
)
#staticmethod
def normalise(expr):
res = sqlalchemy.case(
(type_coerce(expr, Integer()) != sqlalchemy.literal_column("0", type_=Integer), sqlalchemy.literal_column("1", type_=Integer)),
else_=type_coerce(expr, Integer())
)
return type_coerce(res, Boolean())