How should I handle decimal in SQLalchemy & SQLite
decimal, python, sqlalchemy, sqlite, type-conversion
Solution
from decimal import Decimal as D
import sqlalchemy.types as types
class SqliteNumeric(types.TypeDecorator):
impl = types.String
def load_dialect_impl(self, dialect):
return dialect.type_descriptor(types.VARCHAR(100))
def process_bind_param(self, value, dialect):
return str(value)
def process_result_value(self, value, dialect):
return D(value)
# can overwrite the imported type name
# @note: the TypeDecorator does not guarantie the scale and precision.
# you can do this with separate checks
Numeric = SqliteNumeric
class T(Base):
__tablename__ = "t"
id = Column(Integer, primary_key=True, nullable=False, unique=True)
value = Column(Numeric(12, 2), nullable=False)
# value = Column(SqliteNumeric(12, 2), nullable=False)
def __init__(self, value):
self.value = value
Problem
SQLalchemy gives me the following warning when I use a Numeric column with an SQLite database engine. SAWarning: Dialect sqlite+pysqlite does not support Decimal objects natively I'm trying to figure out the best way to have `pkgPrice = Column(Numeric(12,2))` in SQLalchemy while still using SQLite. This question [1] How to convert Python decimal to SQLite numeric? shows a way to use `sqlite3.register_adapter(D, adapt_decimal)` to have SQLite receive and return Decimal, but store Strings, but I don't know how to dig into the SQLAlchemy core to do this yet. Type Decorators look like the right approach but I don't grok them yet. Does anyone have a SQLAlchemy Type Decorator Recipe that will have Numeric or Decimal numbers in the SQLAlchemy model, but store them as strings in SQLite?