> It might be easier if you provide a concrete example of what you are
> trying to achieve (perhaps using the syntax of an existing ORM or using
> pseudo-code) and explain how the DAL falls short.
>
Using SQLAlchemy as data mapper below.
MyItem class (models.myitem):
class MyItem(object):
def __init__(self, name, description, priority, state, creator,
department, notification_users):
self.id = None
self.name = name
self.description = description
self.priority = priority
self.state = state
self.creator = creator
self.department = department
self.notification_users = notification_users
.... (methods that implement MyItem behavior)
Similarly, there are User, Department and ItemNotificationRecipient classes.
MyItem data mapper (persistence.myitem_data_mapper):
metadata = MetaData()
# create mapper between MyItem class and my_items table
my_items_table = Table('my_items', metadata,
Column('id', Integer, primary_key=True),
Column('name', String(100)),
Column('description', String(400)),
Column('priority', Integer),
Column('creator_id', ForeignKey('users.id', ondelete='SET NULL')),
Column('dept_id', ForeignKey('departments.id', ondelete='SET
NULL')),
)
mapper(MyItem, my_items_table, properties={
'notifications' : relationship(ItemNotificationRecipient,
backref='my_item',
cascade="all,delete")
})
Persistence manager code:
def init():
db_engine = create_engine(db_server, echo=False)
Session = sessionmaker(bind=db_engine)
self.session = Session()
def add(model_type, *attributes):
<implementation>
return obj
def get_all(model_type):
<implementation>
return objs
def get(model_type, id)
<implementation>
return obj
def search(model_type, filters, fields, order_by)
<implementation>
return objs
def update(obj)
self.session.commit()
def delete(obj)
<implementation>
Implementing these operations *in a generic way* to
add/delete/update/search data in only one table is rather simple using DAL,
foreign keys make it more complicated. There are several algorithms and
design patterns to handle this generically (eg
http://martinfowler.com/eaaCatalog/ ), but that's exactly what an ORM such
as SQLAlchemy does. How would you implement this in web2py?
--
Resources:
- http://web2py.com
- http://web2py.com/book (Documentation)
- http://github.com/web2py/web2py (Source code)
- https://code.google.com/p/web2py/issues/list (Report Issues)
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