Cannot access column in PostgreSQL table from Python model

Question

I have defined a python class "Students", like this:

class Students(DeclarativeBase):

    __tablename__ = 'students'

    id_ = Column('id', Integer, primary_key=True)

    name = Column('nombre', Unicode(50))
    date_of_birth = Column(Date)

If I do select * from students, I can see all of these columns plus a few more, namely: _created and _updated.

I need to use the values stored in the columns _created and _updated. So I try to access them like this:

#get student with id = 1
>>> s = dbs.query(Students).get(1)

# print its name
>>> print(s.name)
Richard

# try to print when it was created
>>> print (s._created)
AttributeError: 'Students' object has no attribute '_created'

Of course I get that message because the attribute _created is not defined in the model.

How can I access the value stored in the table Students even though it is not an attribute of the class Student?

Answer 1

SQLAlchemy needs the definition of each column it will access. (There are ways to auto-discover by reflecting the database, but explicit is better than implicit.) Add the column definitions to the model. I'm assuming they're DateTimes. You can use default= and onupdate= to provide new values when a row is inserted or updated.

class Student(Base):
    __tablename__ = 'student'

    id = Column('id_', Integer, primary_key=True)
    # other columns...
    created = Column('_created', DateTime, nullable=False, default=datetime.utcnow)
    updated = Column('_updated', DateTime, onupdate=datetime.utcnow)