SQLAlchemy set default value of one column to that of another column

Question

I am trying to write a class for substances which has a name filed (for the name, as commonly used in the lab) and another column for the long name (in case the name is actu

Answer 1

You can create context-sensitive default function

def mydefault(context):
    return context.get_current_parameters()['name']

class Substance(Base):
    __tablename__ = "substances"
    id = Column(Integer, primary_key=True)
    code = Column(String, unique=True)
    name = Column(String, unique=True)
    long_name = Column(String, unique=True, default=mydefault)

Answer 2

In addition to r-m-n's answer if you have more than one column that defaults to value of another one, you can write a helper function to avoid writing many default functions.

def same_as(column_name):
    def default_function(context):
        return context.current_parameters.get(column_name)
    return default_function

# or as a one-liner
same_as = lambda col: lambda ctx: ctx.current_parameters.get(col)

class Substance(Base):
    __tablename__ = "substances"
    id = Column(Integer, primary_key=True)
    name = Column(String, unique=True)
    long_name = Column(String, unique=True, default=same_as('name'))
    created = Column(DateTime, default=datetime.now)
    edited = Column(DateTime, default=same_as('created'))