On Mar 24, 2011, at 5:08 PM, Nickle wrote:
> Doesn't quite work.
>
> What I think is the problem is that when using secondary on the
> association table, there are two foreign keys both referencing a
> calendar. It doesn't know which to pick.
>
> union mapper looks like this
>
> union_calendar_mapper = \
> mapper \
> (
> UnionCalendar,
> inherits=calendar_mapper,
> polymorphic_identity='union',
> properties =
> {
> 'children':relationship(Calendar,
> secondary='calendar_children_table')
> }
> )
oh thats correct, so "primaryjoin" and "secondaryjoin" clear that up, also you
pass the Table object itself to "secondary" without the string:
relationship(Calendar, secondary=calendar_children_table,
primaryjoin=calendar_children_table.c.parent_id=calendars_table.c.id,
secondaryjoin=calendar_children_table.c.child_id=calendars_table.c.id
)
so it knows UnionCalendar id 12 linked to Calendar id 17, put the "12" in
"parent_id", put the "17" in "child_id". Similarly it knows which side is
which inside a query(UnionCalendar).join("children").
>
>
> On Mar 24, 4:29 pm, Michael Bayer <[email protected]> wrote:
>> 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
>>
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