On Mar 24, 2011, at 4:40 AM, Nickle wrote: > I'm trying to implement a Composite Pattern, > http://en.wikipedia.org/wiki/Composite_pattern > > In this case its to represent some holiday calendars. I need to > implement a union calendar that is a collection of other calendars. > > So a straightforward hierarchy. Calendar, abstract as the top level > class. SimpleCalendar that inherits from Calendar. Then a union > calendar that inherits from Calendar, but I need to implement > children, a collection of calendars. > > So its a self referential hierarchy. The point to note is that one > calendar can appear in more than one union calendar, so its a self > referential many to many. Its certain I need an association table as a > result. > > I'm not quite sure how to configure this. > > I'm trying something along these lines > > calendars_table = Table \ > ( > 'calendars', > metadata, > Column ('id', Integer, primary_key=True), > Column ('code', String, nullable=False, unique=True), > Column ('name', String), > Column ('calendar_type', String (20), nullable=False), > Column ('monday', Boolean), > Column ('tuesday', Boolean), > Column ('wednesday', Boolean), > Column ('thurday', Boolean), > Column ('friday', Boolean), > Column ('saturday', Boolean), > Column ('sunday', Boolean) > ) > > calendar_children_table = Table \ > ( > 'calendar_children', > metadata, > Column ('parent_id', Integer, ForeignKey ('calendars.id')), > Column ('child_id', Integer, ForeignKey ('calendars.id')) > ) > > calendar_mapper = mapper (Calendar, calendars_table, > polymorphic_on=calendars_table.c.calendar_type, > polymorphic_identity="calendar") > simple_calendar_mapper = mapper (SimpleCalendar, > inherits=calendar_mapper, > polymorphic_identity='simple',properties={'holidays':relationship(Holiday, > backref='calendar')}) > union_calendar_mapper = mapper (UnionCalendar, > inherits=calendar_mapper, polymorphic_identity='union') > > holidays_table = Table \ > ( > 'holidays', > metadata, > Column ('id', Integer, primary_key=True), > Column ('holiday_type', String(20), nullable=False), > Column ('calendar_id', Integer, ForeignKey ('calendars.id')), > Column ('description', String ), > Column ('year', Integer), > Column ('month', Integer), > Column ('day', Integer) > ) > > holiday_mapper = mapper (Holiday, holidays_table, > polymorphic_on=holidays_table.c.holiday_type, > polymorphic_identity='holiday') > repeating_holiday_mapper = mapper (RepeatingHoliday, > inherits=holiday_mapper, polymorphic_identity='repeating') > simple_holiday_mapper = mapper (SimpleHoliday, > inherits=holiday_mapper, polymorphic_identity='simple') > > However, I'm not sure how to map the relationships with the > association table. > > Points that I think are relevant are > > 1. It's only the UnionCalendar that has children.
apply a relatlonship() to the UnionCalendar mapping, the target class is Calendar, "secondary" is calendar_children_table. > 2. Deleting a UnionCalendar should delete the entries in the > association table, but not the children calendars. This is a given when using "secondary" with relationship. Severing the link between parent and child corresponds to a deletion of the row in "secondary". > 3. Navigation is really only needed from the parent UnionCalendar to > the underlying children calendars. However, having a collection back > the other way might have some uses. just add "backref='parent_containers'" or similar to the relationship(). > 4. For SimpleCalender to its Holidays, I haven't yet implemented the > cascaded delete, but I know how to do this. > > Thanks > > Nick > > -- > You received this message because you are subscribed to the Google Groups > "sqlalchemy" group. > To post to this group, send email to sqlalchemy@googlegroups.com. > To unsubscribe from this group, send email to > sqlalchemy+unsubscr...@googlegroups.com. > For more options, visit this group at > http://groups.google.com/group/sqlalchemy?hl=en. > -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
