Allow dynamic column names in CompositeProperty

[Samer Atiani]

I would like to allow some of the CompositeProperty columns I'm building to get their names dynamically, in a manner that mirrors how columns get their names in sqlalchemy's declarative mapper. The best way I found to implement this behavior is to do the following:

class DeferredCompositeProperty(CompositeProperty):

    def get_column_names(self, key):

        raise NotImplementedError

    def undefer_column_names(self, key):

        for col, name in zip(self.columns, self.get_column_names(key)):

            col.name = name

            col.key = name

class CustomDeclarativeMeta(DeclarativeMeta):

    def __new__(cls, name, bases, d):

        def undefer(k, v):

            if isinstance(v, DeferredCompositeProperty):

                v.undefer_column_names(k)

        for k, v in d.iteritems():

            undefer(k, v)

        for base in bases:

            for k, v in base.__dict__.iteritems():

                undefer(k, v)

        return DeclarativeMeta.__new__(cls, name, bases, d)

class MoneyComposite(DeferredCompositeProperty):

def __init__(self):

DeferredCompositeProperty.__init__(self, <SomeCompositeClass>, Column(Integer), Column(String))

def get_column_names(self, key):

return [

'{}_amount'.format(key),

‘{}_currency’.format(key)

]

Base = declarative_base(metaclass=CustomDeclarativeMeta)

class ExampleModel(Base):

funds = MoneyComposite()

This would result in ExampleModel having the columns: funds_amount and funds_currency automatically without having to specify them directly.

Am I doing this right or is there a better way?

[mike bayer]

not sure offhand - you really don't just want to say:

funds = MoneyComposite('funds')

? sure would be simpler.



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[Samer Atiani]

Definitely simpler :)

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