Question

I’m using the SQLAlchemy recipe here to magically JSON encode/decode a column from the DB in my model like:

class Thing(Base):
    __tablename__ = 'things'
    id = Column(Integer(), primary_key=True)
    data = Column(JSONEncodedDict)

I hit a snag when I wanted to create an extra “raw_data” field in my model to access the same underlying JSON data, but without encoding/decoding it:

    raw_data = Column("data", VARCHAR)

SQLAlchemy seems to get confused by the name collision and leave one column un-mapped. Is there any way I can convince SQLAlchemy to actually map both attributes to the same column?

Answer 1

I would just define the raw_data column through SQLAlchemy and then use Python’s property/setter to make transparent use of data. I.e.:

class Thing(Base):
    __tablename__ = 'things'
    id = Column(Integer(), primary_key=True)
    raw_data = Column(String())

    @property
    def data(self):
        # add some checking here too
        return json.loads(self.raw_data)

    @data.setter
    def data(self, value):
        # dito
        self.raw_data = json.dumps(value)